Well, I guess as a photographer I'm supposed to say stuff like, "team player", or "no problem", or "Extra shot?... Sure we have time for an extra shot." In addition, good production capabilities, fantastic crews, good caterers, etc. are all key. It also doesn't hurt, occasionally, to pop off a great shot or two... or slightly more than occasionally if you're looking for repeat business.
However, I found that stashing a bottle of great bourbon, a box of shortbread cookies and a bar of chocolate in the car, can come in mighty handy when looking to keep a Creative Director happy. I found this out completely by accident... but am happy to share.
