Set-up: Find a surface (e.g. a sturdy box or chair) to elevate your feet on. With the legs together and hips up, establish proper upper body posture with a neutral back. Place your hands next to each other on the floor, with your upper arms are tucked close to your torso.
Lift: Press the chest off the floor until the arms are straight, then return to the starting position. Cue the descent by attempting to 'pull' yourself down to the floor with your shoulder blades.
Emphasis: Don't allow the hips or the lower back to sag. Keep the elbows inside - don't let them flare out to the sides. Use a complete range of motion, bringing the chest to the floor. Don't push the head forward to the floor.