Here are a few tips.
Do a bunch of stair jumps this summer. Just pick a staircase and jump up 2-3 stairs at a time keeping your eyes level and use your peripheral vision to land on the stair. This will train your body and your eyes to have much better form jumping.
Jump on a trampoline a bunch this summer. Your body is not used to floating in the air so you have to get used to it so when you start hitting more floaty park jumps it doest feel as foreign. This will help your body control as you land.
Do a bunch of power cleans. Landing a jump and doing a power clean are basically the exact same mechanics.
Get a yoga DVD. Skiing and Yoga are basically the same thing and the better you get at yoga, the better you will get at skiing. It will help your core, keep you hips open and body stacked, make you flexible to tweak grabs and go a long way for injury prevention.