Here are 3 tips on how to do the perfect push up (sometimes you need to practice in front of the mirror)
1) Get into plank position and make sure your hands are positioned slightly wider than your shoulders. Tighten your core.
2)Lower your body until your chest almost touches the floor, tucking your elbows in as you do. When you're at the bottom, your arms should be at a 45 degree angle.
3)Keep your back flat and do not let your back or hips sag. If you cant do a push-up on your toes yet, don't give up. Do them on your knees with your toes pointed up and you'll still get a great workout.