Approach the jump in a regular, balanced skiing position: arms slightly in front of you and pressure on the tongues of your boots. You may also want to have your skis a bit further apart than normally, but nothing too extreme. Make sure to have your knees bent a bit when approaching the jump.
When you're riding the lip of the jump it's important to keep pressure on the tongues of your boots, otherwise you might go off balance and land on your ski tails or ass. We don't want that happening now do we.
When you're approaching the end of the lip it's time to jump. The kicker does most of the work so don't go crazy here. Just start straightening your legs. If you try to pop too hard, you might end up off balance.
The hard part is over now! Just remember to maintain a balanced position in the air (arms slightly in front of you). Spot your landing, straighten your legs and let your legs do the work when you come down.
That's it, that's how you do a controlled straight air. When you have it on lockdown, it's time to do spins. Pretty much everything I've said applies there too. Remember that waving your arms is pretty much useless, your shoulders and head are what lead the spin. Not arms.
What you do on the lip is the most important part. Focus on that. If you nail that part, the rest of it pretty much happens automatically.
