I just raced in my first one a month ago. Check the website of whoever is holding the race. There will be information on their particular rules. Also check the AMA website for the enduro rules.
As far as getting your bike ready, you may want some aluminum handguards if there are trees. If it is just brush, then plastic handguards are OK. How will you know? You probably won't, so prepare for the worst and hope for the best.
As far as timekeeping, I started on a row with three others. After ten seconds, I never saw any of them again. The guy in front (Dlafleur of DRN fame) was in front of me and the other two were behind me. If you go slow, your riding mate or buddy will have to slow down so you can keep up with him. If you were like me, you will be late, late and late again. I had a roll chart holder, bought the roll chart, pieced it all together with tape the night before and all that. After 1/3 of the way into the race of setting it for resets, I said forget it. Every reset I came to, I just kept riding instead of resting. I was several minutes late. I would just say go out and have a loooong, fun trail ride. I am guessing most people are late rather than early in their first enduro. You will know what's up before you get to the first checkpoint as to whether you are going too fast or not.