I was just looking into this today. I have a left shoulder imbalance I am working on.
Arm bars and waiter walks with a very light weight. See a physio for pain of course.
This is my personal list because they are both easy and effective and don't require bands, equipment or lying down.
I have learned that the shoulder like the hip is a complicated and we can't really separate the overhead shoulder from the scapula, lat, and thoratic mobility. I find it better to do them throughout the day rather than a special mobility session, which I never seem to keep up consistently. Or fit them in for rest periods for lower body work. I don't believe in the physio model where isolated corrective exercises a few minutes a few times a week are doing to do much. A GTG approach where you do them daily and frequently seems necessary (like stretching in general).
As I found out with the military barbell press in my own experience and Gray Cook's admonition not to load disfunction, if you don't have basic shoulder health, you probably should not be pressing heavy or in volume. I got my FMS screen left shoulder from 1 to 2 which is normal (out of 3) by doing corrective exercises. Here they are.
Really easy but effective. Thoratic focus.
Tip: Instantly Increase Upper-Body Mobility | T Nation
1. Google world's greatest stretch
You can also reach back when in the squat position after a goblet squat set during s&s.
2. Max Shank thoratic bridge.
3. Wall slides
4. Spina's arm rotations
Shoulder Mobility with Dr. Andreo Spina
5. Reach behind the back stretch from FMS Test yourself.
FMS - Shoulder Mobility
6. Lat stretch
Posture Correction Exercise | PNF Lat Stretch + T Spine Mobilization This one might even be painful if your lats/shoulders are really tight.
7. Crucifix
Crucifix Stretch do them every hour on the hour at work breaks.
8. Original strength head nods. Do them all day at work. The neck and thoratic spine are connected. You may feel a little click or pop when you do nods. It is like the good crack you can get from foam rolling your spine.
The book flexible steel Jon Engum has good principles and insights as well as a daily routine. For some reason, I can get myself to do exhausting press ladders but not a simple, consistent, daily mobility routine. Go figure.