Once you get the hang of it, you can win like 95% of the games.
In the first ten levels, starve yourself and only eat at 30% hp.
Use corners and other obstacles to your advantage to get sneak-attacks.
Don't equip any unidentified equipment if possible - especially if it is suspiciously high level for the area. It is probably cursed.
Save up your upgrade scrolls until you find some tier 4 or 5 weapons and armor. If you're a mage, just dump them in your wand of fire from lvl 1 with no regrets.
Learn how the bosses attack. The slime hits really hard after charging, so figure out how to dodge or get out of range.
I one trick mage class. I always upgrade my staff as soon as I find a scroll. Once I feel comfortable I'll then imbue my staff and continue to upgrade it.
Is that a bad idea? I've always felt comfortable doing that because I know that my staff will always be my primary weapon.
I've never beaten the game. Only got past the gnome king a handful of times.