Have you joined a club? It is a good idea to hook up with a club and ask them if you can guest ride for this first race.
You will need to bring gas for the entire event. Normally your club will pit for you. They will pour your gas, wipe your goggles and give you liquids.
They will also fish you out of the middle of no-where if you break down.
If you cannot find a club, then you will have to pit yourself. Remember to bring gas, clean goggles (in a plastic bag) and cold water. Park your truck along pit row. Then set your gear out. You don't want to go to your truck away from the gas area.
Get to the race early and sign up. Check out the bomb run. Ride the run and make sure you know the holes and rocks. Be careful and ride the return run on the way back to the truck.
On the start, don't ride wild into the dust. It will be hairy, but ride to the bomb (banner) at a good pace. Don't follow the guy in front, just follow the terrain. Be cautious when you get off the trail to pass, there are rocks with your name on them!
Try to finish the race. Don't try to win. Don't go really slow. Just go out and ride to finish.
Good luck,
RAD DAD
(I used to be in HBMC, they are great bunch of guys)