I was having chronic shoulder pain so I started rotator cuff exercises with a light dumbbell (10 - 15 lbs). Pain went away over a couple of months and has not returned.
Exercises I did:
1. Standing with your elbows straight out to your sides, and dumbbells straight up in the air (your elbow bent 90 degrees), rotate the dumbbell to the front until your forearm is parallel to the floor, then bring it back to vertical. 15-20 reps of these at a light weight, for 3 or 4 sets.
2. Lying on your side, take your top arm and hold the dumbbell near your opposite shoulder, rotate the arm at the elbow, raising your forearm until it is parallel to the floor, then lower it to the starting position. That is 1 rep. Do 15-20 reps with a light weight, for 3 or 4 sets.