HOW: Start facing a door frame or wall. With your elbow bent at your side to 90 deg, push forward into the wall. Slowly ramp up the amount of “pushing” that you do, staying just under the point of pain/discomfort and hold that level of contraction.
FEEL: You should feel the muscles in your shoulder working, especially the front part of the shoulder.
COMPENSATION: Do not shrug your shoulders and use your neck muscles.