Have rotator cuff problems myself, mostly gone now though.
Here's the regimen of rehab exercises I did (And still do once in awhile).
#1. Stand about a foot from the wall, facing it. Hold your bad arm up at a 45 degree angle, with the pinky-side of your hand on the wall. Shrug your shoulder up as high as you can, then drop it. Do this 15 times. It should hurt a little at first if you're doing it right.
#2. link both hands together behind your back, just below the waist. Try to touch your shoulder blades together, without sticking your face forward. Maintain a straight posture. Squeeze 15 times.
#3. Roll up a small towel and put it under your armpit, as far up as you can go. With your arm holding the towel under your armpit, reach back behind you until your hand is resting on the opposite hip, behind your back. Grab that wrist with your other hand and pull to the outside, like you're continuing the reaching behind the back motion of the first arm. It should feel like you are separating and stretching your shoulder muscles... feels really good to me
Next, get a band, of decent resistance (black colour is good).
Tie a knot in one end. Stand beside a door. Put the knotted end into the door, with the knot on the other side, and close the door. Band should be secured perfectly at any height you want.
#4. Band secured at eye level, stand with door on right, wrapping free end of band around right hand.
Start with your arm up if front of your face, in an 'arm-wrestling' position. ROtate your arm slowly, like you are 'winning' the arm wrestling match. Do the negative motion slowly as well. 15 times. Then turn around and repeat with other arm.
Note: You can turn facing away from the door and do this with your arm out to your side, like you're cheering. This the the 'unprotected' version of the 'protected' movement described above.
#5. Same set up as #4, but lower the knotted end to waist level in the doorway, and face the opposite way, so you are rotating arm away from the door. start with arm parallel to floor, like you are about to win arm-wrestling match, and rotate upward, like your opponent is bringing you back up to the start point in the match. Can do protected or unprotected.
Those are the ones I do, hopefull I was able to describe them so you know what the hell I'm trying to say.
Good luck!