1. DON'T lunge across the room. The more you move, the more chances you have to botch your alignment.
DO focus your eyes on a fixed point in front of you—watching yourself in a mirror works well—and place your hands on your hips to stabilize your body and remain balanced. Stay in one place, alternating sides for three sets of 10 to 15 repetitions per leg.
2. DON'T let your lunging knee extend past your toes, which stresses the knee joint and leads to sprains and strains.
DO bring your knee perpendicular to your foot at the fullest part of the lunge. This ensures a full range of motion, maximizing your benefit and giving you the strength to ski longer.
3. DON'T slouch your shoulders. Open them up and stick your chest out. This keeps your body upright and perpendicular to the ground, straightening the spine and lessening your chance of back injury.
DO add weights once simple reps become too easy. Start with a five-pound dumbbell in each hand and increase at five-pound increments as those become effortless.