Band External Rotation

Trains the Shoulders, Infraspinatus and Teres Minor.

How to do it

Anchor a light resistance band at roughly elbow height and stand side-on to it.
Take the band in the hand furthest from the anchor and tuck that elbow against your ribs, bent to ninety degrees.
Step away from the anchor until there is tension with your forearm across your stomach.
Keeping the elbow pinned to your side, rotate your forearm outward away from your body, as though opening a gate.
Rotate as far as the shoulder allows without the elbow lifting, then return under control.

Letting the elbow drift away from the ribs. Once the elbow lifts, the rear deltoid takes over and the movement stops being rotation. A rolled towel held between elbow and side enforces it.
Standing too far from the anchor, so the band is already tight at the start and there is no controlled return.
Using a band far too strong. External rotation strength is a fraction of what the rest of the shoulder can handle — a band that feels almost too easy is usually the right one.
Rotating the whole torso instead of the forearm. If your body turns, the shoulder is not doing the work.