Doubles. Get everything unnatural and then go for double backs/fronts/lincolns. I can do double lincolns and double over flips, only landed them a handful of times, but my goal is to constantly land them. I can do basically everything right and left up to 9. Cork, bio, misty, flat. Oh yea, and if you can't do a double without being double bounced, it doesn't count haha. That's a thing for me because I learned them without being double bounced and I bet half the kids who can do them cannot if they are the only ones on a standard round tramp.