Hey man not to be a dick, but.... there are hundreds of threads with tips and advice on how to do these tricks. But... I am a somewhat nice guy, so I'll give you a copy and paste of what I wrote in a thread on backflips...
"What this guy said. If you can do a gainer off a diving board (facing forward off the diving board, but backflip) then you have nothing to worry about when it comes to skis.
I am also from Wisconsin and the first backflip I ever tried I landed on my head because I was used to trampolines and floating them around and didn't account for all the weight of my boots and skis.
As you approach the jump get low and as you come off the lip pop and thrust your hips to the sky while at the same time throwing your arms up and back, arch your back and keep looking. Keep looking until you see the snow again, put your feet down and stomp it like a G.
Here is a video of me doing it...