You need to adjust to the idea that you are not controlling your skis, you are controlling the posture of the rider. Experiment with very gentle gestures while you're learning the game.
When jumping, take your finger off of the screen before tapping on the top of the screen to stand up. This will make your jumps more explosive.
If you wipeout just before the robot targets, don't be quick to restart the level - there's a chance that your board might carry on and hit them.