Well I can describe to you what he had me do. I don't know it'd work for you, though.
Lay on your back. Hold a soup can in each hand. Lift the cans so that they are straight up in the air, perpendicular to the floor. Then use your shoulders to push them up higher, hold for a few seconds, and then come back down - meaning, your shoulders come back down, not the soup cans. Repeat.
Another thing: Stand in a corner with your back STRAIGHT and your head up. Your hips should be pressing into the corner - not hard, just touching. Take both your arms; bend them at the elbow so that your fingers are pointed toward the ceiling, and your forearm and bicep make a right angle. Move each arm to it's respective wall (since you're standing in a corner). With your elbows and the back of your wrists touching the wall, slide your arms upward and down. Repeat. This one was surprisingly tiring for me!
Again, I don't know if this would work for you. The reason he had me do this stuff was to improve my posture which would THEN improve my shoulder blades. In other words, what I had thought good posture was wrong - the position of my head, neck, shoulders - everything. So even when I made an effort to stand up straight, I looked either like an army officer or a giraffe.
Let me know if you have any questions!