These aren't anything new, but I'd add:

* If someone attacks you and you weren't expecting it, the vast majority of the time that's a fight you're not going to win. Most of the time, the right thing to do is retreat and evaluate the situation (which may mean "getting the hell out of there")

* Return and teleport potions are overpowered. Don't leave home without one.

* Gold is overpowered. Try to keep someon hand for replacing potions (when you use them), healing poison/disease/blindness, etc.

* If you use a client that supports logging, consider logging every session in its entireity. That way you can:

a. Figure out how you got to some area if you weren't the one leading,

b. Refer back to items you may have identified, but most importantly:

c. Review your PK encounters to learn what you did right or wrong.