HOW: Start on your back with your knees bent and slightly spread apart. Tighten up your stomach first, then your glutes. Next, drive your heels into the ground and lift your hips up towards the ceiling. At the end position your knees, hips, and shoulder should be in one straight line. Shift your weight onto one leg, then slowly march from side to side. Make sure you move with control here.
FEEL: You should feel your glutes working to control this motion. At no point should you feel your low back muscles doing the lifting motion. If you feel it only in your hamstrings, try bending your knees a bit more and repeat.
COMPENSATION: Avoid arching at the low back as you perform this.