This exercise is not only one of the most important movement patterns to help you perform daily tasks injury free but it is a great way to strengthen and tone your legs.
Begin standing with your feet together, hands by your side.
Draw you belly button inward. Step forward far enough so that your back thigh and front shin are perpendicular to the floor when you lower down.
Maintaining a good upright posture drop down so that your knee touches the floor, then come back up. Your ear, shoulder, hip and knee should be in line when you reach the end position (viewed from the side).
Push back to the starting position and repeat on the other side. To make the exercise more challenging add weights in your hands.