HOW: Start on the side of a door frame or wall. With your elbow bent at your side to 90 deg, push UP and outwards into the doorway. Think of lifting your elbow towards the ceiling. 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, top and side parts of your shoulder.
COMPENSATION: Do not shrug with your neck muscles, just use your shoulder muscles.