Many people lack internal rotation mobility. Lie on your back and elevate your hips off the ground. Squeeze your scapula together. Place your hands under your back and gently place downward pressure.
Find a ledge, table, or barbell that you can anchor your hands on. Position both arms behind you with your palms down and keep your shoulders locked into their sockets and your shoulder blades retracted.
Position yourself on top of a foam roller lying horizontally across your thoracic spine. Raise your arms overhead and begin arching your upper back over the foam roller.
Place your hands palms down on a desk or a barbell set in a rack. Keep your scapula retracted and your shoulder back.
Position yourself in a doorway or power rack so that you can place your arms perpendicular to your body. Keep your scapula and shoulders back.