Common Mistakes to Avoid

The number of possible mistakes and bad ideas in the game is 
essentially unlimited, and players are constantly finding new ways to 
go spectacularly wrong. There are some particularly popular errors, 
though, that new players should learn to avoid... and experienced 
players should remember to avoid.

Early-Game/Newbie Mistakes and Needs

Always carry some form of healing - Potions of Cure Serious Wounds or 
Cure Critical Wounds are the most common options in the early game. Do 
not be too slow in recalling home if you start running out of healing 
potions - it's better to lose a fight or miss out on loot than to die.

Always have some way to escape dangerous situations; in the early game, 
this will likely be a healthy pile of Scrolls of Phase Door or Scrolls 
of Teleportation, or (ideally) both. Early-game characters are 
extremely likely to need Teleportation if they enter the wilderness. 
About the only characters who shouldn't carry Scrolls of Phase Door and 
Teleportation in the early game are Berserkers, who cannot read 
scrolls.

Do not neglect the quests that town buildings offer. They are a fairly 
fast (and fun) way to level up, and tend to provide comparatively good 
loot. Many characters (including practically all melee-class 
characters) can do the Thieves' Hideout quest starting at character 
level 1.

Do not wander too deep without some way to deal with confusion. As 
early as dungeon level 10, you should always have Mushrooms of Cure 
Confusion and/or Potions of Curing or Clarity with you. Even then, 
monsters who melee to confuse remain highly dangerous, as they may 
immediately re-confuse you as soon as you cure the confusion, giving 
you no opportunity to escape. If you've found any Potions of Speed, 
always carry at least one (and ideally more) for emergencies like this. 
Later, unless you're playing a Berserker, Staves of Teleport will allow 
you to teleport away while confused.

Do not worry too much about traps, except in situations where you have 
specific reasons to expect them (like in the Thieves' Hideout and Orc 
Camp quests, or because a monster just cast a trap-creation spell). 
Early-game traps are a minor nuisance rather than deadly, and in the 
unlikely case you are killed by a trap it will probably be a very new 
character you haven't invested much energy into. Accordingly, it's no 
big deal if you have no means of detecting traps. Even if you have a 
Rod of Detect Traps, don't be shy about dropping it if you need that 
inventory slot for something else. Only start detecting traps regularly 
when you get your first Rod of Detection; even then, worry more about 
monsters and objects than traps.

Do not bother with digging into treasure veins for money, at least if 
you're playing with selling on - there are faster and more productive 
ways to get rich. Digging for money can work in the early game in 
no-selling games (where gold finds are increased and opportunities to 
earn money in other ways are more limited), especially if you have some 
item or power (like a Wand of Stone to Mud, a cheap digging spell or a 
+5 weapon of Sharpness) that makes it exceptionally easy to dig.

Do not forget to pack enough food and oil for long journeys.

Do not underestimate items that confuse, even the humble Wand of 
Confuse Monster. They make many fights radically safer and easier. 
Potions of Booze can confuse monsters if thrown!

Do not be too slow in escaping or healing if you start running low on 
HP. If you escape too late, a device-fail or an unlucky teleport into 
another dangerous area might kill you. (This mistake is very much not 
exclusive to newbies or the early game, but it's good to get out of 
your system early!)

Do not fight monsters in melee if they have highly dangerous (or 
annoying) melee attacks but no way to hurt you from range.

Try to reach new towns and dungeons in the safest way possible - stick 
to roads, minimize the time spent in dangerous areas, and travel 
through the overworld rather than the raw wilderness. Not only are you 
less likely to get lost on the overworld map, but travelling there is 
safer too - though you should still prepare for ambushes!


Middle-Game Mistakes and Needs

Always detect regularly. Make sure you know where the monsters are.

Always have at least one level of Free Action, ideally two (or even 
three in the late game). Free Action is not absolutely needed in the 
early game but becomes necessary in the middlegame. Do not enter the 
Old Barracks quest or the Old Man Willow quest without Free Action.

Always have a source of either See Invisible or Telepathy.

Always carry a Wand of Teleport Other (unless you're a Berserker). 
Teleporting the enemy is safer than teleporting yourself, because you 
might land into another trouble spot - also, there are a few enemies 
who can follow your teleports! Note, though, that some monsters can 
resist teleportation or are even completely immune to it.

Always prepare adequately before entering a quest. Quests are a leading 
killer of characters. Take larger piles of cure wounds/healing potions 
into quests than into dungeons.

Always haste yourself when you're about to enter a fight or quest you 
know will be dangerous. If you feel this makes you use too many Potions 
of Speed, simply avoid fights that would require hasting to win safely, 
until you have more Potions of Speed or some other source of Haste 
Self.

Store most of your Potions of Healing and Potions of *Healing* at home 
- you will need them more later than you need them now. Nevertheless, 
do carry at least *some* Potions of Healing for emergencies; and in the 
late game, start carrying one or more Potions of *Healing* too.

Do not invest all your stat-ups in a single stat. No character lives 
entirely off one stat - melee characters need Strength, Dexterity and 
Constitution; pure spellcasters are very reliant on their casting stat, 
but will still want some Strength for carrying items and Constitution 
for staying alive, even if they do no melee at all. Investing several 
consecutive stat-ups in a single key stat is not necessarily a bad 
idea, but as the stat cap (somewhere between 18/70 and 18/130) is 
approached, the returns diminish rapidly. The best returns are offered 
when a stat's base value is close to 18.

Do not completely neglect items useful in niche situations, especially 
if you know where those situations will happen. You might not carry 
Potions of Resist Heat and Cold all the time, but it's still a good 
idea to take some to the Smaug and Utgard-Loke fights. Similarly, 
Potions of Vigor will be highly valuable in the Micro$oft quest, and 
Staves of Starlight can be handy in Old Watchtower.

Do not underestimate mushrooms, especially Mushrooms of Cure Poison 
(the game's most effective means to neutralize poison) and the 
always-handy Mushrooms of Fast Recovery.

Still do not underestimate items that confuse. In the middlegame, this 
usually means a Staff of Confuse Monsters, though if you're really 
lucky you might find an early Staff of Confusing Lights!

Prefer loot you might one day wear (or otherwise use) to loot that's 
only good for selling, even if the latter has a higher nominal value. 
Do not ignore items that meet your needs, even if their nominal value 
is low.

Remember that the melee bonuses on a Ring of Combat only apply to the 
hand you're wearing it on; if you have no weapon in that hand, the 
bonuses are lost.

Always keep backups at home for key devices that might get destroyed.


Late-Game Mistakes and Needs

Always have enough speed, and haste yourself for dangerous encounters. 
Double-moves are a leading cause of late-game death, and low speed 
makes them much more likely.

Always choose appropriate escapes. The best way to deal with a 
dangerous situation can be any of Phase Door, Teleport, Teleport Level, 
Teleport Other, Destruction or Dimension Door (or simply Healing or 
*Healing*), depending on the particulars of the situation; do not rely 
too much on any one method.

Do not forget about reforging. Do not use mid-level, 50K weapons or 
armour as reforge source items. (As long as you're reforging into 
lower-value slots, a 40K bow, a 30K pair of gloves or even a 25K lamp 
will give better results more cheaply.)

Do not hang around in open areas where many dangerous high-level 
monsters simultaneously have you in their lines of sight, unless 
there's a reason you know it to be safe (for example, if the monsters 
are safely confused Cyberdemons and unlikely to recover for some time).

Do not stop carrying Potions of Healing when you find your first Staff 
of Healing. Staves of Healing are great, but potions are still needed 
for emergencies. At the same time, try to keep such emergencies to a 
minimum.

Remember to drop Staves of Destruction, Staves of Genocide and Wands of 
Annihilation before entering a quest. They are all highly useful items, 
but they won't work in quests. (The same goes for Scrolls of 
Destruction, Genocide, Mass Genocide and Teleport Level, and spells 
with the same effects.)

Do not underestimate high-level monsters, especially uniques. Nodens, 
in particular, can kill a character even faster than the Serpent of 
Chaos. Teleport Nodens away on sight or destruct him - unless you're 
really, really sure you want to fight him...

Do not underestimate high-level quests, especially the Spawning Pits.

Do not accidentally destruct the Serpent of Chaos (or another questor 
you're fighting, like Oberon) - it will restore them to full health.

Do not enter the Serpent fight with a full stomach (or anything near 
it), unless you know you can keep the fight short or have some way to 
empty your stomach. In a long Serpent fight you might need enough 
mushrooms and potions to make you gorged, costing critical speed.

Above all else...

DO NOT get overconfident. It's easy to start feeling complacent on a 
character who seems invincible, but no character is too strong to be 
killed.