I separated my shoulder a few years ago and it bothered me for a long time mostly because I didn’t take care of it like I should have and kept doing Brazilian Jiu Jitsu and Grappling while it was healing. I re-injured it many times and although it is healed a 100% now I have a small dip in my shoulder from it.
I mention the separated shoulder because every once in a while i feel the shoulder get a little more unstable (like today) and I turn to an exercise tool that has proven reliable to me in the past. My gym has several different type of resistance band, very similar to these, and I simply place one end on a fixed object a little below shoulder height, back away to a comfortable distance and start moving the band in as many different directions my shoulder can possibly go for 10 reps each.
Start with the lighter resistance bands first! Once the shoulder starts to stabilize from the muscles pulling the shoulders together you can gradually use the heavier resistance bands. I know everyone is different but this single exercise and mild stretching has done wonders for rehabilitating my separated shoulder!