Never pull without the whole party.
Gonna say an obvious one, don't be the tank if you're not the tank.
Give-ing up is for quitters!
You are responsible for your own derps.
Up your commendations by being a good sport.

Never abandon your party.
Gonna get deep here; everyone dies and it's okay.
Let your DPS/healing/tanking speak for itself.
You should really Greed that item if you're already wearing a higher ilevel.
Down that path is a boss, be ready for it.

In case anyone is confused by what I mean.

:3