Hold a dumbbell in your right hand — 10 pounds is a good starting point (I use 20) — and place your left knee and left hand on a bench. Your hand should be underneath your shoulder and your knee should be underneath your hip. Your spine and head should be in a neutral position.
Engage your core, relax your shoulders, and extend your right arm towards the floor. Do not rotate your torso or let your shoulder lower towards the floor.
On an exhale, pull the dumbbell up with control, driving your elbow towards the ceiling. Do not rotate your torso.
On an inhale, lower the dumbbell back down to the starting position. This completes one rep.