Strength and Conditioning - Probably the best thing you can do in your spare time. Can improve your skiing ability whilst also protecting you from injury
Core Workouts - Helps avoid back injuries, increased control over rotation, and increased strength in general skiing
Leg Workouts - More control and protects you from busting your knee's
Stretching Before Skiing - Surprisingly helped me SO much this year. I have had no problems with anything and it makes you feel good whilst skiing
Diet
Coffee/Red Bull before you go skiing - Works for me
Big Breakfast - When you are hungry, you are tired. When you are tired, you risk injury
Sleep - " "
ALWAYS WORKS FOR ME