First and foremost you need to learn on how to ride a motocross bike. Let me layout the basic experience levels for you.
I'm guessing you're starting out, so you would be a beginner. Here are the different types of classes.
A - Pro
B - Semi-Pro
C - Experienced Rider
D - Beginner
Now, for the basic skills for beginners, you will need to learn on how to jump, and go threw corners quite fast. I would recommend going to a track, and watching more experienced riders ride, and do what they do. Watch how their hand rolls in and out of a corner, and see how they work the clutch. If you can, buy motocross books on how to ride, or even videos.
For beginners, you cannot triple so, that's one good thing about being one, but the bad thing is, they're very new to riding, and can crash easier so, I would watch yourself and KEEP YOUR LINE! No matter what, keep your line when you race, if you mess up on a jump, and crossrut, you may go down with a rider on top of you.
I hope this helps a bit, good luck.