I would make sure that your pecs are stretched out first of all. I think the most important one that works for me is rolling out the teres major/teres minor/infraspinatus area which is basically the armpit. You might look weird doing it but it works so who cares.
You could also get a tennis ball/lacrosse ball and work on the "trigger points" on the front and back side of the shoulder to help loosen it up.
I'm sure there are tons of other things you could do but those are just a few. Hope it helps.