I've been doing them a hell of a alot recentley but now i'm laying of them, it's all about throwig your weight forward. I found that when about to leave for the front gap make sure your tyer it pinching on the edge to give your more bounce. At first you will probbaly start nose diving quite a bit but thats normal and happens, still happens to me sometimes. If i was you i would start learning on really small things first like i don't know get some pallets and make a few little things just to learn on. I really preload alot when leaving for the gap to front wheel and thrust right up and jump with the bike, then i would like jump the bike forward so i'm going straight for the gap and my front wheel it on the other side then just ease your brake lightley and let the back wheel just ease it's self on. Just get practising them and you'll get them, Once you start getting them there'll just start getting bigger and bigger and after a period of time you'll starting doing them to wheel swaps and doing them on higher things up. Get out there and practice