load the bike coming up the face of the jump... then gun it off the entire face of the ramp.. when the suspension starts to unload you kinda pull up, straighten your legs and back to where you are arched backwards and the the most important thing is to keep your head tilted back as if you were looking up and back at the sky...
I've never pulled one succcesfully and haven't even tried since my BMX days but those were the pointers i got..i always had a hard time commiting my head to be tilted back the entire way. but your body will follow your heads lead, so you just have to go at it 100%
good luck andwatch some vids of other people to see the correct posture...get some practive vids up for us...we fiend for some big air wipe outs :lol:
The most important part of a backflip (I've never done one on a pitbike but I've landed thousands of Mosley's and backflips on my skis) is to arch your back like your trying to touch your goggle strap to your back then when your rotating and can see your landing stay focused on the landing so you don't over rotate bro. Hope it helps.
PS Metzger gave some very helpful tips on Stunt Junkies for executing a sweet backflip. Try to find that footage on Discoverychannel.com or you tube.