Be prepared to not want to race MX again, a hare & hound is easily the most fun allowed under the law.
A lot of what you'll experience will depend on the dust conditions. If it's dusty the start becomes very critical. You should get to practice the bomb run, usually 1-3 miles or so. Be sure and practice several different routes on the bomb run to find the smoothest one. Practice your dead-engine start technique. I assume they'll be using a banner-type start. If so, keep in mind that it takes some concerted effort to drop the banner, so keep your eyes riveted to one of the two people that'll be dropping the banner. As soon as you see them start to make that effort to drop it, kick and go. Your next key is getting to the trail in front of you before the guys in your immediate vicinity. If you do and can avoid getting in anyone's dust, obviously that's a huge advantage. You should have at least a couple miles (if not several more) after the bomb run before you run into any single track.
Make sure your arms are warmed up before the race, as arm pump can be a crippling problem at higher speeds. And a hydro pack is more than a good idea, it's absolutely critical. If possible, try and drink that water as early in the race as possible, you'd be amazed at how quickly you can become dehydrated.
One of the beauties of desert racing is there's not much of that having to move out of the way BS. For the most part you'll have plenty of room to get by the guy in front of you. When the situation presents itself off-roaders are generally pretty good about moving over.
Pacing yourself - and especially ratcheting it back a couple of notches if you get in dust off the start - is quite important as well, depending upon your level of fitness of course.
Prepare for big fun, and also be prepared to be absolutely amazed at how fast some of those guys go over such nasty terrain. Be sure and post on here and let me know how it goes! If you have any questions let me know. I've never raced an H&H in Nevada but have quite a bit of experience with races in Southern California.
Good luck!