One tip that I sort of stumbled upon in my last game, although it is probably a no-brainer. Stairs are your best friend going down and coming back up. If you find the stairs early and decide to keep exploring, always know your quickest path back to the stairs. If you are in need of some rest to heal up, go to the stairs and stand on them while you are resting. If a nasty monster (griffon) happens along, you can run down the stairs to get away from him without losing a single hit point. Similarly, if you run into something you are not sure you can take out, run back to the stairs and head down. If you feel like pressing you luck, fight a tough monster while you are on the stairs. If the battle goes poorly, head on down to the next floor and live to fight another day. I used this strategy on every floor I could in my last game and I know it saved me numerous ugly endings.
-Dave