Lessons learned the hard way was a huge Rodney entry. It was so large that it had to be removed from the database because Rodney would become unresponsive to everyone else whenever someone requested the entry. For a while it was hosted by GreyKnight, but now that the wiki exists we can put it where it really belongs.
Go ahead. Leave autopickup on (Shift+2). It's convenient right up until the point you walk over that cockatrice corpse without gloves. Or get overencumbered right when the swarm of killer bees arrives.
Don't mess with player-type characters on the Astral Plane. Yes, there's only something like a 5% chance they'll be spawned with the Vorpal Blade. Yes, it only has a 5% chance to instantly behead you. Yes, you will die. Every time.
Don't try to cancel your own spellcasting by pressing Escape, especially when polypiling. Skipping the direction prompt releases the magic power to the previous direction!
When you get a blessed scroll of genocide, @ means you, even though you're a gnome.
Forcing the lock on the chest with a blunt weapon on the castle level isn't the best idea. Kicking it isn't such a good idea either, if the object you're expecting happens to be made of glass or crystal.
Sleep rays bounce, and elves don't start with sleep resistance.
Beware the hallucinating pet arch-lich. (Make sure that that black light over there blows up in your face and not your pet's.)
Never sacrifice something you can't touch! Attempting to lure a cockatrice onto an altar for sacrifice with the idea that you can do so without touching it will cause you to develop a stony appearance without any chance of eating a lizard.
Never eat tins in shops whilst wielding potentially expensive artifacts.
When polypiling, be careful with where you aim. In particular, don't hit that damn chest with goodies - if it polymorphs into a non-container, ALL CONTENTS ARE LOST.
When you have laggy connection, NEVER type the next command before you see how the previous one ended.
When running from a nasty monster, go back the way you came.
Be careful of what items are marked as 'y' and 'n' in your inventory to avoid confusion with yes/no prompts. For example, trying to eat something on the ground while levitating by typing 'ey' quickly will have disastrous effects if your inventory contains 'y - a cockatrice corpse'.
Be careful of what items are marked as direction-moving keys in your inventory, in case you miss a key, so instead of 'ahky' (apply h-a key north Unlock the door? yes) you hit 'aky' (apply k-a wand of cancellation Really break your wand of cancellation? yes)
When hiding in a shop to recover HP, make sure to rest instead of search to avoid finding (and waking) mimics.
Make sure comestibles (esp. rubber chickens) aren't assigned 'e', wands aren't assigned 'z' or 'a', potions aren't assigned 'q', scrolls and spellbooks aren't assigned 'r', tools aren't assigned 'a', weapons that might be cursed aren't assigned 'w', armor that might be cursed isn't assigned 'W', rings that might be cursed aren't assigned 'P', etc.
Wield the cockatrice corpse when you're already in position to attack (you won't be moving into any unknown squares). Otherwise you will fall into a pit or spiked pit on your way to your victim and be stoned instantly.
When the ground around you looks the same except for being a different color, examine it with / or ; before stepping there.
Don't try to polymorph a merely annoying monster just to get it out of your way; save your charges (or mana) for things that are just about to kill you; the creature it becomes might be something deadly. (StormEagle, blue jelly => ice devil)
If someone throws an egg at you, it might have been a cockatrice egg - don't skip through the messages about stiffening and turning to stone as if they were ordinary battle spam, if you don't want to become a statue.
If you're trying for #conduct weaponless, just leave pick-axes on the ground. Don't even bother to put them in your BoH. Use wands of digging instead (which are not wielded). If you're going for #conduct pacifist, wield a cream pie and never let go. Rely on 5 to move.
While trying to tame something using charm monster that can resist, you'll probably gain a lot of pets. Naming them *all* will help keep you from sacrificing a pet (since corpses retain names) and losing your 50 points of protection.
Get a second or third opinion. ALWAYS.
Don't eat anything while standing on Medusa's corpse. You WILL fatfinger it and suffer a legendarily stupid stoning.
Always kill shapechangers when you see them. If you don't they turn into bad things that will kill you.
argiopeweb -- Minotaur in Soko3
Demin - Black Dragon Gnomish Mines lv 2
RegalStar - Archlich in Soko4
Don't stone-to-flesh statues from a bones file. They are likely to be well-armed and armored.
If a human zombie dies on your altar during a sacfest, move the human corpse away before trying to sacrifice anything.
If you see any messages pertaining to a swamp, do NOT blithely skip along the level. You WILL hit the water, and all your stuff WILL get blanked.
Monsters will follow you through your quest portal. Engraving on the portal square doesn't work.
If you're dipping potions into a fountain, don't typo and dip your bag of holding. The RNG will curse it. Every time. (Actually, don't dip things into fountains at all - instead, dig down on the fountain and bathe in the resulting pools.)
When in Sokoban, and you are at the fringe of death, do not try to teleport away using a scroll of teleportation. Sokoban is a no-teleport area, which will result in a few more hits from that monster you are trying to flee from, possibly resulting in your death.
When you solve a Sokoban level and open the door at the end of the hall, it will be packed with monsters. One might just be a Nymph who will charm you, steal your Wand of death, fail to teleport, then use it on you.
When attacking a gas spore, make sure your pet isn't within the range of the explosion when the spore dies. It will count as if you killed the pet. This also applies to aligned Priests - losing the only co-aligned temple in your entire dungeon is a real bummer.
If you want to create Excalibur in Minetown, make absolutely sure that there are no guards around (or that you have a pet strong enough to deal with them). Even if they aren't in sight, they will somehow sense you and get angry at you, and killing them counts as murder.
Don't try to polymorph at experience level 1 or 2, unless you like being killed by unsuccessful polymorphs.
Don't zap your kitten with a wand of polymorph unless you're prepared to risk the consequences of killing it yourself (System shock).
Standing on a burned Elbereth and reverse genociding dragons to create DSM is a great idea... unless you have teleportitis.
Pause every time you see a monster. Watching the contents of your inventory, or what you are polymorphed into, is free. Thinking of a tactic is also free. Going toe-to-toe with a footrice when you're poly'd into a master mind flayer is priceless.
After spending hours of hard work and effort to descend into Gehemmon, only to be swamped by monsters, remember to check your status as often as your inventory. Scrolls of genocide may be great escape items, but only if that umber hulk next to you isn't looking your way! (And no, your AoLS will not save your sorry self here!)
Werecreatures are considered human. Sacrificing werecreatures while not chaotic is not a good idea.
AVOID foocubi of opposite gender when levitating over water in Medusa's level using boots. Drowning is not kinky.
Chameleons leave brown corpses. They can also impersonate monsters which leave brown corpses.
If you drop your weapons and armor to go for a scroll-blanking swim in the castle's moat, please take care where you leave those items lying around. Chasing down a master mind flayer that's made off with your +7 Grayswandir is not fun when you're unarmed.
When you get to the castle level, do not burn Elbereth on the drawbridge and fight the monsters there. A wand of striking will kill you instantly, and it won't be fun.
Destroying a drawbridge with force bolt kills everything in the same way like closing the drawbridge. Including you.
Even if you've been struggling with containerless inventory management for 10,000 turns, and you've finally got a bag of holding from a wish, don't get all excited and just throw everything into it. That pesky wand of cancellation will go in last, and then you're screwed.
If your luck is negative, or even if you think it MIGHT be negative, DON'T WISH UNTIL YOU FIX IT!
If you're confused in a shop and standing next to the shopkeeper with your very promising character, keep doing nothing for as long as it takes. Yes I know it's only a 1 in 8 chance. Yes it will kill you. The same may happen for blind characters without telepathy. The m prefix to movement commands is safe - you will say "Pardon me" instead of attacking.
A bugle is not a good tool for a knight to use to wake sleeping monsters - especially in the mine town.
Never use force bolt in a level with a shop (you hear the chime of a cash register) if you haven't explored the area in the direction you're shooting if you can't pay for broken things, unless you can fight the shopkeeper.
Never eat an unknown tin whilst hallucinating. It WILL be cockatrice meat.
Engraving with wands is useful. Unless you get the message "The bugs on the floor stop moving!" More often than not, it will be a wand of sleep, but rarely it can be a wand of death. Don't zap it on walls that can reflect back to you (all of them). It will be that wand of death.
Even if it is a wand of sleep, you're still leaving yourself wide open to be maimed while helpless.
If you Branchport into Fort Ludios, you may very well land in the area just outside the inner keep and get swarmed by everything. While it's (generally) not a fatal error, it can still get rather annoying when you can't deal with about fifty creatures one-on-one.
Training escape spells by repeatedly casting "jumping" is a sound strategy -- except in Sokoban. Especially if you plan to zap your wand of wishing soon afterward.
Don't polymorph an air elemental in Slash'em. You will get a very fast baby dragon that is even more powerful.
Do not pray on an aligned altar when you are starving. You stomach won't change, but your prayer timeout will.
When you accidentally get snakes from a fountain, run. Don't fight, run.
In SLASH'EM, yes, you *can* sacrifice the Hand of Vecna. And yes, this gets rid of it permanently.
Go ahead - leave auto-pickup on. It's handy until you walk over that footrice corpse without gloves.
In NetHackW (graphical version) please remember to turn off auto-pickup. It's nice until you find a statue. You wonder why you can't pick up anything when You see here 57 gold coins. There is nothing here to pick up. Or You see here a statue. You can barely move a hand's reach with this load!
Be sure to identify wands before zapping them at enemies, especially if you're zapping an unknown wand of make invisible at a nymph!
Stand back when casting fireball unless you want your pets and belongings to burn.
For crying out loud, don't kick down doors if they have an engravement in front of them! Even if it's ??o?? f?? I???t???.
If you find a dead end, don't hold down s. It'll just make things worse if you encounter a monster and are still searching.
When you find a small mimic in a shop, be sure to attack it, not the shopkeeper! There's no way to say that you meant to hit the mimic!
Similarly, when attacking a mimic with wands or spells, check your rebound path every single time. The shopkeeper does not stand still while you're fighting.
If you're multi-tasking with NetHack, be sure you're in the chat box with your friend(s) and not still on the Net Hack command prompt. "r u playing nethack again?" yes (y: Unknown extended commande: What do you want to eat? [acdsR-?*]s: A cockatrice corpse. Do you want your possessions identified?)
Engraving with your hands in the dust is fine unless your Elbereth happens to be E¦bereth.
Just because you survived that rolling boulder trap does not mean you or your pet will survive it again.
If you fall through a trap door into a vault without a pickaxe, don't keep saying that your name is Croesus, as the vault doesn't have any kind of food in it.
When casting force bolt, be sure that there are no pets, shopkeepers, guards, etc. behind what you're hitting.
Don't put every single damn piece of armor, gloves, or shoes you find on! Sure, they might not be cursed, but when you do put them on, they'll be cursed. Every single time!
When it comes to genociding (Master) Mind flayers, if you're a dwarf... enough said.
Make sure to remove that ring of conflict you might be wearing before you enter a shop.
If you're kicking things off traps, make sure you aren't low on HP and are strong.
And also remember to press k if you want to kick things off a rolling boulder trap in the Gnomish Mines.
When surrounded by resurrecting rock troll corpses, don't quaff an unidentified potion. It will be polymorph, and you will become a grid bug.
In SLASH'EM, make sure you beware creatures hiding under items. It could be a deadly asphynx, which has the ability to petrify you and cause an easy-to-miss YASD.
Unless you are in immediate danger of dying, don't break an unidentified wand. You will be killed by a blast of magic.
Even if you happen to be wearing a ring of polymorph control, don't try to polymorph (quaffing sinks \...) when you are a low level (like XL1) - you risk death from system shock or from level drain after feeling like a new man/elf/orc.
If the RNG gives you another bag of holding after you already have one, leave it alone. Don't carry it around as a spare. You will space out and try to put one of them in the other.
When trying to get crowned so that your god will give you a spellbook of finger of death, make sure your luck is actually maxed before casting create monster a couple hundred times.
When you've been fighting hordes of monsters as a master mind flayer, remember that your stomach is now quite full. Do not try eating anything, especially a randomly generated newt in the lower levels of Gehennom just to try and get that one extra MP for the heck of it.
If you enter an area (say, perhaps the zoo on the way to kill the Wizard) with cockatrices and weapon-wielding monsters (say, perhaps a troll), back off and make SURE you've got a blessed unicorn horn or a lizard corpse handy in your inventory. Be a good Boy Scout and always be prepared.
Carrying around a lot of potions in your main inventory is a bad idea. You will step on a magic trap and die when a blast of fire causes all of your potions to boil and explode right after you've wished for blessed +3 silver dragon scale mail and the Master Key of Thievery.
So wait, I'm NOT supposed to use that fireball scroll while hallucinating?
Don't eat eggs unless you're sure of what's in it. Just because you haven't seen any cockatrices yet, doesn't mean the egg is safe.
Don't bang on the keyboard, you'll just be angrier.
Don't rest on the keyboard either!
Attacking a floating eye isn't always fatal... unless there are strong monsters nearby (there are).
Collecting useful items from bones files is great! Reading/Using anything immediately after isn't.
Yes, pressing any directional key counts as 1 turn, no matter what!
Have a laptop? Move carefully.
Just because your laptop doesn't have a numpad, it doesn't mean you can't move diagonally. Then again, normal numbers hate laptops that play NetHack. Especially if you're confused.
The castle level is a cruel, cruel place...Trust me...
Don't try to play 2 NetHack games at the same time. Just don't.
Skip the Gnomish Mines and come back when you're more powerful, or you won't get past level 3 of the main branch and die in the Gnomish Mines.
Never quaff from the fountains on the Oracle level, ever. (In fact, don't do anything to the fountains there.)
If you're listening to music while playing NetHack, don't, don't, DON'T press buttons (especially directional keys) in time to your music, you'll miss your YASD.
In SLASH'EM as an ice or flame mage, don't youpoly into a dragon when you are wearing armor. Unlike lycanthropes and doppelgangers, you will break out of it. And unlike regular poylmorphs into them, your dragon scale mail is not preserved.
An organized pack helps. a - primary weapon, d - pick axe, g - unicorn horn, etc. Arrange to taste.
After clearing a screenful of monsters involving c, leave for the level for 250-300 turns, to let the corpses rot away.
Finding a blindfold from a bones file while having intrinsic telepathy is great! Now don't get all excited and put it on immediately after just to "try it out", because you'll be "trying it out" much longer than you'd like.
Archons' dazzle is incredibly annoying - lens are nearly worthless.
Get greedy; get killed.
Don't try that genocide scroll until you've BUC tested it! A room full of Liches at level 3 leads to YASD!
Don't try to teleport on a no-teleport level, especially while in combat.
Also, don't let the demon princes summon Demogorgon. Really, just don't.
Don't polymorph pets on the wizard's level before finding the vibrating square.
Some artifacts will blast you when wished for. It is good to be prepared with 41 hit points before making such a wish, but don't make the mistake of immediately donning said artifact as soon as it is in your hands.
He's called MASTER Kaen for a reason. Prepare accordingly.
For the love of Thoth, NEVER launch a fireball at point-blank range! No, not even with fire resistance, you'll still fry your armor, potions, and scrolls!
Never, ever, ever, ever, ever attack a floating eye in melee. Sooner or later, you'll do it while wielding your dwarvish mattock instead of your Magicbane, which means that you won't actually kill the darn thing in one hit, get paralyzed by its passive attack, warp someplace unsafe because teleport control doesn't work when paralyzed, and then be shredded to bits by winter wolves and tengu.
Don't leave that wand of digging lying around just because you don't think you need it. The nymph that just stole all your stuff will be more than happy to make use of it for a clean getaway.
If you think it's a wand of polymorph, don't go zapping peaceful hobbits with it. You don't want to suddenly stand next to a minotaur at XL:10 only to find out your wand just ran out of charges.
When using an amulet of magical breathing to cross water, don't forget that the oilskin sack you stuffed your rustables/blankables into will leak if cursed.
If you do not have a greased helmet, NEVER attack a (master) mind flayer in melee. Having sustain ability doesn't prevent amnesia.