Have a look at damons new vid, theres 2 angles of a hook. Your weight needs to be as high and over the bars as possible when you hit the wall with both wheels at the same time. You need to try to jump and get the 'over the bars' possition before you hit the wall, once you hit you will feel the bike continue up by itself if you have the body position right. All you need to do is push down on the bars at the point of contact and lift the bike through, a bit like a tap at the end body position wise. Hope that helps a little bit, its best to ride with someone who can do it so you can watch again and again and again