Self massage to the shoulders can help to relieve tension from the neck area. This can have a noticeable improvement on your shoulder pain! As a basic guideline you can begin by massaging the small band of muscles at the base of your skull, then grab and squeeze your trapezius muscles, then pull and knead the muscles around the top of your shoulder blade, base of your neck and on your back. End off by kneading first the one side of your neck and then the other.
One thing I would say is to start gently, in case you get a reaction to your own treatment and are left feeling a little tender. Once you get used to gentle massage, you can go a little deeper and more regularly.