Backside boneless on tranny?
I found when I was learning them, I was trying to extend them to far, making it really hard to get the board back under me. Basically what you want to do, is roll up like you're just going to pop up onto the deck. Then make sure to turn all the way around. It's easy to let yourself just turn 90 degrees. This wont be a problem later, but for learning you'll want to do the full 180. Then grab and think of it like you're doing a melon grab, try to keep the board more under you, as opposed to kicking out behind you for the style points. Then really all it is is hopping back on. I learned em to tail first, and that sort of fucked with me taking them straight in at first. Once you've got it up on the coping, eye your landing, jump and get that shit back under your feet.
Also, if you're having trouble getting it back under you, try grabbing different spots. I know some guys kind of nosegrab it, where as I grab backside.