Always be willing to learn; always be gracious, humble, and willing to help. Never think you're better than anyone else, and treat everyone on set the way you yourself would like to be treated. Keep a good sense of humor, and support those around you (a rising tide raises all ships).
Generally; don't be a dick and build your network as best you can. DO your best work on EVERY SET, regardless of the rate, and own up to your mistakes, if any. Most importantly, try not to stress too much. Some jobs will go great, some will be a disaster, it happens. I also highly recommend always maintaining perspective, it's far too easy to get lost in the good and bad of the moment, but you have to have a larger view, I think, to keep from going crazy.