Ski racing can put your knees in precarious positions, so having strong glutes and hamstrings will help protect the knee.
To get started early on your squats, go deep or go home! Half squats (thigh parallel to floor) work out the quads, but full squats (all the way down) work the posterior chain (back) as well as the anterior (front) of your legs.
For a detailed analysis on why the deep squat is desirable, check out this article:
If you can’t get into a deep squat (below parallel) without lifting your heels, this article will tell you why. For the how, consult a certified personal trainer.
Mastering squat technique is essential for the competitive athlete. Even for the weekend warrior, a good squat will help you get stronger, more mobile and prevent injury.