You want to rehab a shoulder injury as soon as possible. If not, it can freeze in a bad position to limit motion, cause pain, arthritis and destroy your posture.
Before starting motion with your shoulder, check your posture to make sure you exercise in a good position. Then start with stretches first by causing enough tension without causing pain. Then add in strength exercises with simple weights to improve strength.
Start you rehab in this order:
Corner Stretch for Rounded Shoulders
3 Shoulder Exercises for Shoulders
Wall Push up
These exercises will stretch, then strengthen your shoulder to keep it pain-free. The bonus is your posture will improve to tolerate the physical and static (such as sitting or standing) stresses of your day to keep you strong and relaxed.