I was an instructor in Japan for a couple of years, and the biggest mistake people seem to make when they are beginners is trying to do too much on the jump before they are even off the ground - particulary if they are trying to do a 180 or 360. They end up twisting themselves and stacking on the actual kicker. The steady takeoff from the kicker is vital to keep you vertical in the air. Start with some grabs first, then go from there. I'd say it's best to do jumps (as a beginner) on a red (medium) run.