Expect the first lap to be fast -- really fast. Don't blow yourself up trying to hang at the front, unless you have expectations of finishing in the top tier. Pace yourself, or you'll be praying for a mechanical after the first lap so you can drop out.
As a mountain biker, you might have a tendency to want to ride everything -- steep run-ups come to mind. Remember that your goal is to get around the course as quickly and efficiently as possible. I've seen really stubborn mountain bikers trying to grind up a ridiculous inclines while everyone else blows by them on foot.
Also, don't get fixated on the guy in front of you, otherwise you'll never move up. Think four or five riders ahead, and aim for catching them.
Whatever your goals, just keep in mind that everyone is suffering as badly, if not worse than you are. Cyclocross is a war of attrition. If you don't blow-up early in the race, you'll be able to start picking off riders one-by-one as the race slogs on (sometimes seemingly forever).
By the way, a handup is whatever a spectator is holding out for you to eat / smoke / imbibe / bank. Dollar bills, whisky shots, cheap beer and cigarettes all come to mind. You can expect your results to be inversely proportional to the amount of handups you accept.
Good luck, and have fun!