Begin in a standard Push Up position, with one hand directly underneath the shoulder, but the other arm extended straight out to the side, using a basketball or other elevated surface for support. Feet together, PPT (Tuck Tailbone), whole body engaged.
Bend the working arm, keeping the elbow tucked tight to the body, and don't allow it to drift backward. The shoulder should move forward as you descend.
Keep your hips and shoulders level, resisting rotation by engaging your whole body, squeezing your glutes, and staying tight throughout the movement.
Pause at the bottom, and drive through the working arm to return to the start, with the arm fully extended. Repeat for repetitions.
Minimise involvement of the assisting arm, and keep as much tension as possible on the working arm, while executing a full range of motion and keeping that elbow tucked in to your side.