I generally run an instance once or twice depending on how bad it is *cough* WC *cough* then I go and get all of the quests for said instance and I burn them down.

Running the instance the first few times is more to get a little bit more gear and xp, the only reason I get the quests later is because I don't like the instance grind and if I have the quests it forces me to go and run the instance once more.