for skiing get your legs strong and(for park anyways) be light.
For your legs, build up with squats or deadlift. Strong legs from this=stronger knees=longer days/less chance of injury. Helped me a lot.
when that is going well, don't be a fatass. If you are currently a total fatass with no intent on eating fruit, than become an alcohalic to the point that you throw up everything in your stomach =).
Arm workouts do not help skiing. FWI I am 6'0", 160lbs, max deadlift was 345(thats 3 45lb, 1 10lb, and 1 5lb weight on each side of the 45lb bar) last time I did that a bit back, haven't tried to max squats in a long time.