The push-up is a basic exercise, but also one that sees a great amount of sloppiness and poor body control. The body must remain rigid from the head to the feet. Do not allow the hips to sag or elevate, and don't dip the head down. Keep the upper arms within about 45 degrees away from the sides of the body. This is not only a more sound movement for the shoulders, but also maximizes the range of motion. Bring the chest all the way to the floor without relaxing into. Ensure the elbows fully extend at the top of each rep and the shoulder blades protract.