1. HP, HP, HP. I don't care if you're a wizard, a barb, a rogue, or anything... if you don't have enough HP to survive basic attacks, then you're the one losing on DPS and heals and stuff. Start at a base of 14 CON.
2. Fortification is important! No, not fortitude. Fortification can turn a nasty 200 point crit hit into a measly 50 point hit. Heavy Fortification can help you survive a lot more.
3. Don't move when you enter Hound of Xoriat.
4. Learn self-sufficiency. Carrying a stack of remove curse potions allows you to easily remove those nasty curses and get back into the fighting.
5. Pay attention! Don't bring trash unneccessarily to your party that knows they can't handle it. Also, your HP can be low but if you don't pay attention to it, then you'll be dead because you didn't know that you were at 30 HP.
That's all I have.