One exercise I like a lot is one called "blackburns." This an excellent series of static holds for improving the strength of your rotator cuff and upper back.
Here is a video of these from DeFranco's Training:
Go very light on these - 5 pound or 2.5 pound plates are a good place to start. You are working very small muscles in your upper back and shoulder, and you don't want to strain them, you want to train them.
And a different, unweighted version of Blackburns, from Charles Staley:
大会結果：5/21 JBJJF 第8回中国柔術選手権 | アダルト黒帯で白木大輔がWゴールド
9 minutes ago