I haven't done one on a dirt bike (are you crazy? I just bought the bike October 22), but I do them on horseback over jumps almost every time I ride (6x a week). So...I hope this will help.
Start over comfortable (little) jumps, of course, but try only letting go of only ONE hand. Like someone also said, you could also start by hovering both hands over the grips. I'd personally start with one hand (prolly hovering over the grips), and then work my way up.
I experienced that you have a GREAT tendacy to lean backward and bump into the seat. But, this may be inapplicable to dirt bikes b/c with horses you have to take-off without hands, and, in my case, without stirrups either...going over a 3'3"H x 3'W fan-oxer jump, which is fairly large for horses (thats like no hands AND no foot pegs jumping 10' high straight-up...VERY TOUGH!). With that, you MUST keep your center of gravity directly over the horse's; otherwise, you'll be enjoying the taste of dirt...trust me ;)
I'd imagine that it would be the same with dirt bikes and you have to stay with the center of gravity on the bike or you won't stay on it.
So, there you have my two cents at your disposal. Keep practicing, whatever method you choose. It'll help you become a better rider, I bet. Sorry if I rambled abour horses for a moment!
Jade
ps. Don't forget to visit my website! :)
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Female-Piloted '93 KX80
All About Dirt Bikes, the site devoted to the KX80!
[This message has been edited by jadestrada (edited 04-19-2001).]