Reminder warnings when you're close to level up if there are...
1. Poison enemies on the map you could kill
2. Mana Burn enemies on the map you could kill
3. You don't have a deity yet and Pactmaker has been uncovered. (Or Binlor, for that matter)
We know how many of each level gets spawned in any given dungeon; keep a list of uncovered monsters of each level, and killed monsters of each level, so you don't go exploring for "I wonder if there's any more level 5 monsters out there?"
If you worship Dracul, and come across a HALPMEH glyph, have red flashing lights saying "Convert from ground! Don't even pick up, it'll disappear!" (Seriously, I screw this up every time). Similar warnings should happen if you worship Jehoira and picked up GETINDARE.
For Transmuter: memory of which tiles used to have walls on them, and which ones never did. (This can be the difference between exploring in a direction that will uncover new spells and enemies...and exploring in a direction that was always a bank of walls).
Keep track of how many glyphs are left out there, and how many stat boosters are left out there, and how many shops are left out there.
If you worshipped Dracul, the boss is undead, you're fighting the boss, and you have 4 or less piety, again provide bright red warning klaxons.
Seriously, it's this memory stuff that trips me up; I can do the math (I like doing the math).