Check out a ewe-tube video called “The Best Scapular Stabilisation Exercise with Dr. Evan Osar.”
The doctor goes through some common moves for external rotation and thoracic extension, and explains why they aren’t effective until you get the serratus going to control the scapula. Then he shows some good moves to learn how to integrate the serratus and scap tilt into the rest of your motions and movements.
In post #958 I linked my favorite moves to do with good scap position to increase shoulder ROM.
In post #4 of this thread I link some of my favorite exercises to do for individual small muscles while using good scap tilt.