Prepare two platforms (benches) separated by a distance approximately as long as your legs. Sit on one bench and put your hands in the correct position. Hold on to the bench so that the radial part of your hands point toward your body. It is only your palms, not the whole hands that lean against the bench. Put your feet on the second bench with your heels in a shoulder-width position. After you have put your feet on the second bench, shift your body over the floor with support on your hands and heels; i.e. lift yourself up from the bench and keep the body lifted between the two benches. Your legs must be perpendicular to your torso.
Slowly lower your body by bending at the elbows until you have lowered yourself far enough to where there is a 90-degree (approximately) between the upper arm and the forearm. As you bend your elbows, they should be pointing backwards, not sideways. All the way through the motion, keep your torso upright and along the bench. Once you have reached the sufficient angle, go back to the starting position by contracting your triceps (elbow extension). Breathe in as you go down; breathe out as you go up (to the starting position).
Make sure your platforms (benches) are in the correct position.
Be careful about the position of your hands; as you support yourself, they should not be far from each other and elbows should be tucked in.
Your torso should be perpendicular to the floor all the way through the exercise.
Avoid concentric engagement of upper trapezius muscles (lifting your shoulders up).
To simplify the learning process, try several repetitions with your feet on the floor and watch yourself sideways in the mirror.