Just got my first Dirtbike in Jan of '12. Well, used to have a XR80 I rode in a field when I was 13 or so. Started trail riding on it and have since done 2 Hare Scrambles. One of the things I've noticed is how helpful/nice everyone is. I'm still really slow so run/ran the slowest class and got lapped at my first one by everyone. 2 Mechanicals didn't help with that but I finished a lap and got last place so I was happy.
You'll waste more energy and time picking the bike back up trying to go fast than you will by slowing down a bit and maintaining a pace you're comfortable with. Also you're there to have fun, the guy behind you banging off the rev limiter and whooping at ya is prob there to win, let him by. I've pulled over and just taken a break to let the whole A and B group pass me as I knew I'd just be getting in the way. Also had multiple guys make sure I was ok while they passed.
Also agree with the take a break advice if you need to. You'll see others doing the same. Some stop to pee, some stop just for a breather and a drink of water, you won't be the only one.
My experience thus far is it's good times, good people, and good fun. Slowly but surely upping my stamina for riding further/longer and plan to actual train for this years season and maybe not get a last place at some point.