Here is a set of movements you can do back to back to give you not only a good shoulder workout but also increase (or maintain) your shoulder mobility.
As much as possible move through this sequence with as little rest between sets as you can. The less resting you do, the more it will function as a strength workout.
That being said, if you find yourself compromising the movements or getting hunched over, shruggy or otherwise showing signs of poor alignment or bad posture, take a break and shake it out!