The problems: Bending forward, not squatting low enough, allowing your knees to cave inward.
How to fix it: Toddlers squat with ease. For the rest of us, though, squatting with good form is a tall order; years of sitting — or more accurately, slouching — in front of a TV, in a car, at a desk, etc. have ruined us for this once normal and effortless movement pattern. Furthermore, modern life rarely asks us to perform a low squat unsupported, so most people lack the core strength and hip/ankle mobility necessary to comfortably assume this position.
• Start by making yourself “tall and skinny,” standing upright with your feet hip to shoulder width apart. Your weight should be on your heels — evenly distributed between left and right — throughout the movement.
• Keeping your back flat, push your hips back, bend your knees, and lower your body until your thighs are at least parallel to the floor (or as low as you can get them). Keep your head aligned with your spine (you should be looking at a spot several feet in front of you on the floor at the bottom of the move), and don’t let your knees cave inward.
• Reverse the movement to return to the starting position.
For those who have trouble dropping all the way down into a full squat due to poor ankle and/or hip mobility, withhold adding weight until you can perform the bodyweight version using proper form.