Do some light rotator cuff exercises to strenthen the muscles surrounding the joint. Kind of tough to explain but here we go...
1. Stand side on to a cable pulley with adjustable height. Your left shoulder pointing at the machine. Take your right arm and imagine you're holding your ribs after someone has given you a good crack. This is the start point for your right arm. Holding the cable handle rotate your right arm away from your body. Visualisation: go from holding your bruised ribs to as if you're pointing a gun from someone. Your right elbow should never leave your side.
2. Stand with arms straight out to your sides at ear level. Bend you arms 90 degrees so your arms are still level with your ears but your hands are slightly in front of you with your palms facing down. This is the starting point. Rotate your shoulders so your hands are in the air, as if someone is pointing a gun at you and you want to show them you're unarmed. Your upper arm (bicep/tricep) should never move up or down, this way the rotator cuff does all the work. Now hold some light weights in your hands while you do this action. (can use cables as well)
(This one you may have trouble with, try it without weight first)
3. For the previous 2 exercises, reverse the starting and finishing points (you'll also have to reverse your body positioning) and instead of 'pulling backwards', try 'pull forwards.'
Most importantly remember that if there is an inordinate amount of pain (I'm talking a sharp stabbing pain, not just a bit of discomfort - you should feel the difference) in a joint the surrounding muscles have a tendency to 'switch themselves off.' This means that other muscles take over, muscles that aren't supposed to be recruited in that particular exercise. This gradually causes an imbalance and you end up with tendonitis or other overuse injuries.