I’m not a doctor or any sort of medical person, but I do have two old rotator cuff tears that require constant exercise, so I’m pretty familiar with shoulder PT.

Yes, pull your shoulders, and thereby your shoulder blades, back and down slightly, so they’re flat against your back and stabilized. Don’t squeeze them hard together.

How I was taught to figure out how far back and down was enough was to take a two to four pound weight and hold it straight out in front of yourself. If you don’t already reflexively stabilize your shoulder, then pull your shoulder blade back and down until it feels stable. This will cause your shoulder to rise and pull back a bit. It’s hard to describe but you’ll hit a point where everything just feels like it’s in the right place. It’ll feel easier to hold the weight and more stable. That’s the position to use for rotator cuff exercises.

On a related note, I’m a HUGE fan of spinning hula hoops on your wrists for rotator cuff rehabilitation and strengthening. I have some lumps of scar tissue that cause my shoulders to click and pop for certain movements, which happens to include most rotator cuff exercises. The hula hoops minimize motion and focus on building stabilizing strength.