Lie flat on a bench, with your arms straight over your shoulders, holding dumbbells.
Bend your elbows until your arms are bent at approximately 90 degrees.
Extend your elbows back to the start position and repeat.
Moving elbows around.
Using excessive momentum.
Rushing repetitions.
Hang from the bar with an overhand grip, spaced just wider than shoulder width.
Bring your legs up to be level with the hips.
Slowly lower back to the start position and repeat.
Swinging around.
Using momentum to kick legs up.
Dropping on the way down.