Well since I'm a motocross guy I can give you a little insight, but it may not be 100% accurate. So far from my RC Jumping...it works though ;-)
1. Leave the jump ON the gas, don't gain speed and just coast off the lip. Keep the gas on, even if it's just a blip.
2. If your car is setup to do full brakes at idle, you're going to front flip (Yes I found this out with my buggy already!)
3. You can change the pitch of the car in the air by using gas/brake. If you give it gas your front end will go UP. If you apply the brakes, your front end will go DOWN. Laws of physics really. You're either increasing the rotating mass causing the rear to drop, or tapping the brake and transferring that stopped rotating mass forward which lowers the front of the car.
4. Hit the ramp straight on! Unless of course you WANT to barrel roll the car/truck. (Yup tried this one too!)
It takes a little practice, but give it a shot and start on small jumps to get the feel for it then work your way up to the bigger ones. Granted with an RC car, you won't kill yourself, but you sure can break some expensive stuff! Ideally you want to maintain some speed when you land and land with your rear wheels slightly before your front wheels (depending on the jump). When it hits the ground...give it some gas again so smooth out the landing.
Hope that helps?