I've had 3 surgeries on my left shoulder for rotator cuff problems. For my physical theropy we did all sorts of things.
The ones that helped me the best (in my opinion) were with small weights. Say you're doing your left shoulder. Lay down on your right side and grab a 5lber or so to start with. Keep your elbow tucked in to your left hip. lift the weight and hold for a certain amount of time then drop back down. the key is keeping your elbow stationary. Thumb is up (facing your nose) and the movement is straight up, right about belt line or so.
Doing somthing like a leg-lift, but with your arms instead. laying down, have a small weight and lift the weight about a foot or so off the ground, keeping it up for a particular amount of time. You can do this; thumb facing body, thumb up, and thumb away (away if you don't have serious risk of subluxation).
I'll see if I can find my paper of routines I used to do when rehabing.
When I got better, the standing dumbell lifts to the front and to the side were good for me. Also, try it across body too, that was a rehab exercise.
Lastly, in a pushup like position, balancing on a ball when you're about at half up/half down. These help to build those small core muscles that we often forget about traing and will make a significant improvement in strength overall.