Playing it for over a decade.
I primary play the huntress, so all these are from that perspective:
* only eat when necessary, that is starving or early on level and likely lot of enemies.
* your first upgrade scroll is for your permanent bow, upgrade the scroll, then apply it to the bow
* there is a specific path for enemy's approach, always
* use the seeds with statues and mimics in there presumed path
* ranged attacks where possible
* before walking into a well of health, put on all the cursed items, they will become uncursed
* in the shop order of buying is next bag/satchel, then food (even with horn of plenty), ankh (unless you are super confident), thereafter as augment your weaknesses with potions of healing, scrolls, rings, wands from the store
* when picking up things make sure you pick up in order of most preferred to least preferred. Items last picked up get stolen first.
* always try to "trap" enemy in a door. i.e. they stand in the doorway
* if you get a plate armour, dump every, single, upgrade into it. No questions.
* drink potions early, standing near door and water
* a broken honey pot & health potion brewed is worth more than individually
* upgrade potion of experience and scroll of transmutation, then use it to pick and improve a tiers of abilities.
* the frost and fireblast wands can turn your raw meat into good food. With frost, the meat needs to be against a wall or something. Fireblast just torches everything.
* rooms with traps - if they are single target traps, go to the furthest spot, then rest or make noise to bring the enemies in. Throw stuff on the trap triggering attacks on the enemy. for the avalanche rooms, drop something in the doorway, step back then throw stuff on the traps.
* enraged gnolls, just walk away. There is no arguing with someone who lost self-control :)
Good luck! You will need it.