I like the idea of improving range of motion to make skill development easier. Put to gether a stretching routine for shoulders that addresses every muscle group that leads to or from the shoulders, ie. chest...lats...intercostals (muscles between the ribs)...and trapezius. Your routine should use light/comfortable resistance over the complete range of motion while repeting the motion enough times to warm the muscle and then fatique it. Once this has been done you can do some static stretches mostly to feel the almost instant improvement in motion. This improvement will not last more than say 1/2 to one hour, so some brief static streches or motion streches during the work-out session are necessary. I saw Nikki"s post and that exercise is a good stating point. but I would like to se it put into motion by standing on a rolling board and slowly pushing your hands down and towards your hips to roll yourself to the spotting block. Use an assistant to help you roll if you are not strong enough.
I also like GikiGirl's exercise but I would put it into motion by moving with very straight arms from a verticle start position to a position that fully opens the shoulders, reverse and bring the arms back to the verticle. Repeat for multiple reps (10-20). Use only enough weight to "feel it" until you are accustomed to the exercise. Never use a weight that you won't be able to complete 8 repetitions with.
An extra benifit to the "motion" concept is that it will increase muscle strength and and muscle comfort at the extreme of the motion range.