Confidence is key to jumping. If it's not there, you're going to bail. That's pretty much a given.
How do you build confidence? Hit the same size jumps you were hitting at your local park or indoor place. Get comfortable in a new park, on the same sized jumps, and then move up from there.
I suck at jumping, I over think it and get wigged out (and I've been boarding for 21 or so years now). The only way I'll hit 30 ft+ kickers is when I'm in "the zone". The way I get in the zone is to take a few laps through the park hitting the small and medium jumps. I get my legs under me, get comfortable with the snow conditions, etc. Then I head for the large jumps and hit them without overthinking it. I have knuckled a couple 30 footers because of the wrong takeoff speed, and live to tell about it, so don't put too much fear into jumping. Yes you can get VERY hurt, but if you think to much about it, you WILL get hurt.
Always reach for a grab in between the bindings, even if you don't successfully complete the grab. The motion of compressing yourself in the air helps stabilize you, and then you bring the landing gear down to absorb the impact.