Stand tall with your feet shoulder width apart. Lower yourself as far as you can by pushing back your hips and bending your knees. You can stand with a chair behind you so that you can aim your hips toward the seat; this will help keep your torso upright and your thighs stay parallel to the floor. Make sure you press your weight down into your heels. This will help stop the knees coming over the toes. Finally, try to keep a natural arch in the lower back. Make the exercise more challenging by adding some weights.