Raise the ball to a pike position with your hands on the ground and your feet balanced on the ball. Once in this position you pull your legs toward your upper body and repeat this 10 times. However, your pole plant technique can make or break a run through the bumps or short turns in the steeps. That is why it's good to work the lats, triceps, and upper back muscles. With a strong upper body you can stabilize and correct while allowing the feet something solid to turn against.
Strength training helps athleticism as well as helps prevent injury.
Flexibility refers to the range of motion at a joint or joints and strength will help control those movements. Most avid skiers like to work on their quad muscles and forget about the opposing hamstring muscles. Work the opposing muscles and spend extra time on the trunk this season. Timing is everything and in skiing if you don't have quick feet the skis will soon be taking you for a ride instead of the other way around. Quick lateral movements can be ingrained by placing a pillow on the floor and hoping sideways from foot to foot while maintaining a balanced upper body.