Get into a push-up position either with your toes flexed or knees on the floor. Lower yourself until your chest nearly touches the ground; then push back up. As you straighten your elbows, feel your spine press toward the ceiling (to help engage your back muscles as well). Do as many push-ups as you can (this is called exercising to failure, and it's what helps build strength in your muscles). If these are too hard, just hold your chest off the ground without moving.