What kind of bike and how big is the jump? If you're just beginning, you probably cut throttle before you hit the lip and that is just the recipe for an endo. Keep at least constant gas when you launch.
If the jump has a kicker at the top, that will throw the rear up no matter what, and you just have to compensate by staying back on the bike and giving it some gas.
The final possibility is that your rebound damping in the rear is set too low or the spring too hard and the back of the bike jumps up because of that. So measure sag numbers first to set the spring correctly and then start playing with the clickers if you truly think this is your problem.