HOW: Place a rolled towel underneath your toes. Shift your weight to stand just on that foot. Keep your knee straight, push through your toes and slowly raise your heel off of the ground. Slowly lower back down and repeat.
FEEL: You should feel your calf muscle working. You should also feel the bottom of your big toe stretching.
COMPENSATION: Keep the knee straight. Make sure the towel is underneath your toes, not the middle of your foot.