Stand in split standing (if you are pulling with your right hand have your left leg facing forwards). Hinge forwards at your hips, with your knees bent, spine in neutral and rest your body weight resting on a lower surface with your left arm. With your right arm hanging down towards the floor in front of you, pull your shoulder blade back first until it's fully retracted, and then pull through with the elbow, keeping it close by your side and keeping your shoulder blade pulled back the whole time. As you pull through with your elbow don't let the shoulder roll forward. To return, let your arm start to straighten forward but keep your shoulder blade back and not let it pop forward. When your arm is almost straightened out you can begin to let your shoulder blade come forwards again.