The teres minor is the smallest of the rotator cuff muscles and is narrow and elongated in shape. From Wikipedia: “the muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula and inserts at both the greater tubercle of the humerus and the posterior surface of the joint capsule.” Everyone understand that? For those without a college level understanding of anatomy, the teres minor attaches on the back edge of the shoulder blade and connects to the big knob of the humerus and the back of the shoulder joint (see the picture below).
The primary function of the teres minor is to prevent the shoulder socket from sliding up as the arm is lifted (i.e. keep the shoulder down as you raise your arm), and help with adduction of the arm (bringing it towards the body). It also helps to rotate the humerus laterally/externally along with the infraspinatus. In fact, the teres minor often blends with the infraspinatus.
To target the teres minor, incorporate external and internal rotation exercises with abduction. These can be done with either dumbbells or bands and in many different body positions (prone, back lying, or standing), but since the teres minor is smaller, keep the resistance light. Additionally, you will want to focus on keeping your shoulders down and not shrugging during the movement.