I've partially separated them in both shoulders at least seven times(rugby). If you don't let it heal properly it can become recurring, such as in my case. Physiotherapy is your friend, don't comeback too quickly from the injury either.
Once healed I've found chin-ups are the best thing to keep them strong. Yoga helped as well but I've been told by athletic/physio/osteo therapists that any exercises that really work the stabilizers in your shoulders should do the trick.
Sleep can be a bitch as well, if I sleep the wrong way on either shoulder I can be in pain for the day.