Right now, I have a weak left rotator cuff. My right rotator cuff is extremely strong, as I was a baseball player for a long time. Basically, right now I have to train my rotators daily, while not doing bench, flyes, pullups or any shoulder work. It really sucks, because bench was my weak point.
Anyways, here's what I do.
theraband shoulder presses on the ground
The last one is where I lay on my back, feet flat on the floor and as close to your butt as possible. Wrap a theraband around your butt and grab both ends with your hands. Try to keep your wrists and elbows on the ground the entire time. Push up and out to a V formation, while keeping wr and el on ground. At the top, shrug your shoulders to your ears. It's really weird looking, but it forces your shoulders to stabilize and it is a good trap workout.
Also, you can look into doing figure 8's with dumbbells overhead. I've done these before, and damn they make your shoulders tired.