Let's see - DO: tip your waiters & cabin steward, at least as much as recommended; have the attitude that you are going to have a good time, even if every little thing isn't 100% perfect; get a massage
DON'T: complain a lot to other passengers if something isn't right (but DO politely take it to whoever is in charge, like the purser's office or the maitre d'); feel you need to eat all the courses offered - skip one each dinner; and DON'T miss the boat!!