Dumbbell Lateral Raise

Trains the Lateral Deltoid.

How to do it

Stand holding a dumbbell in each hand at your sides, palms facing your body, with a slight bend in your elbows.
Stand tall with your feet hip-width apart and brace your stomach so your torso stays still.
Raise both dumbbells out to your sides in a wide arc, leading with your elbows rather than your hands.
Stop when your arms reach shoulder height and are roughly parallel to the floor.
Lower under control back to your sides. Fight the weight on the way down rather than letting it drop.

Using too much weight, so the shoulders shrug up toward the ears. Once the upper traps are lifting the arm, the lateral deltoid has been bypassed and the exercise is doing nothing it was chosen for. A lighter weight lifted by the arms alone does more than a heavier one the body swings.
Swinging the torso to start each repetition. If you have to lean back and then forward to get the dumbbells moving, momentum is doing the first half of every rep. Slow the movement down and reduce the load.
Going far above shoulder height. Past horizontal the shoulder blade has to rotate for the arm to keep travelling, so the traps and serratus take over. That is not wrong, but it is no longer a lateral raise.
Rushing the lowering half. This is a small muscle through a short range, and the controlled descent is a large fraction of the total work available. Take two or three seconds to come down.