Reverse Fly with External Rotation

Trains the Shoulders, Infraspinatus and Teres Minor.

How to do it

Sit on the end of a bench with a light dumbbell in each hand, or stand and hinge forward at the hips.
Lean forward so your chest is close to your thighs and let the dumbbells hang below you, palms facing each other.
Set a soft bend in your elbows and hold it.
Raise both dumbbells out to your sides in a wide arc until your arms are level with your shoulders.
At the top, rotate your forearms upward so your thumbs point toward the ceiling — this is the external rotation the name refers to, and it is the part most people leave out.
Reverse the rotation, then lower the arms under control back to the start.

Skipping the rotation and doing a plain reverse fly. The rotation at the top is the entire reason to choose this variation over a normal rear delt raise; without it the infraspinatus and teres minor are barely involved.
Rotating from the wrist rather than the shoulder. The whole upper arm should turn, not just the hand.
Loading it like a rear delt exercise. The rotation component only works at a weight the external rotators can actually turn, which is much lighter.
Bending the elbows to lift more. Fix the elbow angle at the start; a changing angle means the load is being pressed rather than raised.