Do a couple prep jumps and swing your arms up really fast.
When you're doing your tuck, the "set" is like a hole. Pull your legs through the hole.
Do not let go at the end.
The tighter you pull, the better your chances are at landing.
But the main thing is JUMP. Just jump like the prep jump (^ described up there ^) then pull your legs up when you're at the top of the jump. The flipping will happen naturally from there. Just pull and hold on. And try to overrotate. Don't punch your legs down or let go of your thighs when you're about to land, you've just landed, or you feel like you're going to bust.