You wrote "without falling off". Interesting way of explaining a sad/bad jump landing. I usually think what happens just before that, like smashing a wrist, etc.
I am no FMXer but some tips I can think of:
Wear the right safety gear or do not bother.
Start small. As in "walk before you run".
Start with friendly landing zones. eg. no pot holes.
Don't bother being adventurous with bad bike suspension.
Experiment with the throttle (up ramp, in air and landing).
Experiment with body weight positioning.
Experiment with standing and sitting on the up ramp.
Experiment with rear brake tapping mid air (to get nose down).
Dont jump in too low a gear, else you will it your rev limit before you can get the nose back up. Also your landings will be more harsh if you cannot up speed the rear wheel (even just a little) just before touch down.
The less friendly is the track/jumps then the bigger you need your wheels to be.
If you develop the front/rear bike height control, then you are in good shape to get more adventurous because you can make corrections. It also helps if you bike has some good engine grunt.
When you crashed, it sounds like you got sideways or "crossed up" a little on landing and maybe throttled on when not expecting to. So you then became like a rag doll passenger instead of the pilot. Maybe (just maybe) it could have been prevented if you looked more forward and thought about positioning your body with the plan of throttling on intensionally to ride out of it. Starting "small" is the best thing to remember. Then you can botch jumps literally on purpose and work out what you and your bike can and cannot do. Stay with the bike and always try to save it. Only on a real come up short double wall slammer would you bail. Damn I hope I never have to make that decision. Funny thing is you usually know how things are going to turn out just after you are airborne. Which means the take off is key. Really get your bike sorted too if it's a shitter! Have fun.
Here is something to aim for:
YouTube - James Stewart MySpace Whip