Mike,
Well...as a freestyle wanna-be, here's what I can offer.
First and most importantly, you just don't go out and perform a stunt or a trick. It takes skill, not courage.
The best thing to do is to take it one step at a time.
The first step is to get real good at doing nothing but jumping the bike. So good that you can hit the same jump over and over again and consistently get the same results. This means you get a perfect even "float" from the bike each time. Expect about 50 to 100 jumps before it really starts to feel right.
In the process of this, you'll need to get the feel of when the bike is still rising, and when it's falling. Same thing with your body. You'll want to make sure you can judge the up and down energy of you and the bike. If not, you may not be able to get back on the pegs before your landing. Not a prettty picture.
Your next step would be to start lifting one leg at a time. Jump, lift the right leg out, return, and land. Same for the other leg. Then you can advance to two legs at the same time. Try it sitting down, and try it standing up. This may take another 50 to 100 jumps.
Then you can advance your skills by simply getting your body and legs higher and higher in the air.
You'll notice that the real good FMXers are very smooth with their bikes. This gives them the foundation and confidence to extend far from their bikes and be able to get back home before they land.
One other tip is to almost always try and stay with the bike. Many people don't realize that when they toss the bike coming off a bad jump, that they are still 20 to 30 feet in the air. And even if you land out of control, at least the bike's suspension and soft seat will help dramatically soften the blow. And when you learn to stay with it, you'll also learn better recovery methods.
So be patient, and wear plenty of protection.
Good luck!
DaveJ