HOW: In a seated position on the ground or table, have your legs straight out from your hips. Rotate your foot outward, keep your knee straight, and squeeze your quad muscle pushing down with your knee. From here, keep the squeeze in your quad as you lift your heel and leg up off of the ground and back down for the prescribed amount of reps.
FEEL: You should feel your quadriceps muscles working as you lift the leg off the ground.
COMPENSATION: Keep your foot rotated out as you lift up. Make sure you keep the quad contracted the whole time.