Last year during my physique prep, Anne Sheehan prescribed an exercise called "Floor is Lava." (I love that she named it something simple and not the actual scientific name, lol).
Basically, lying face down with your arms straight at your sides, extend arms overhead, without them touching the ground. Seems so simple, yet I loved the way it fatigued my shoulders at the end of an upper body day. Plus, I felt the range of motion really made my shoulders feel good. Don't go fast on these... take your time and really focus on the movement. (These are shown first in the video.)
More recently, being coached by Paul Oneid, he prescribed Prone Swimmers. Now, I'd be lying if I said I loved these. These are similar to the floor is lava exercise, but this time you'll start with hands behind the back, elbows bent, backs of your hands on your low back.
As you'll see in the video, lift the elbows and hands off your back first. That alone is the killer of the exercise. Then extend the arms straight and bring them overhead, then all the way back down, finishing at the start position on your back. Again, take your time with these.
Let me know what you think!