XC races are similar to time trials. You go all out for the number of laps required. There is virtually no drafting and not much strategy.
The MOST important this is a pre-race ride to scope out the course and to find the fastest line in the technical sections. Don't ride your race during the pre-ride. Save your good stuff for the race. My last race of the season this year featured a sandy, 30 ft. blind descent. I approached it nervously on the pre-ride, but negotiated it okay. Later in the race I rode it 3 more times. The confidence I built during the pre-ride reduced my nervousness during the race.
Another thing to keep in mind is that speed and fatigue make easy trails look hard, and hard trails look impossible. Stuff you're comfortable with on a trail ride at home becomes really hard when you're going all out, in traffic and you're tire. Just concentrate harder. If you let down mentally you'll be on your butt in no time.