Stand straight holding the dumbbells by your sides, palms facing forward.
Bend your elbows until the weight is up to shoulder height.
Slowly lower back to just before full extension and repeat.
Using momentum from the body.
Fully locking out elbows.
Elbows moving around too much.
Holding a dumbbell lay down on a bench with your head at the end of the bench.
With a slight bend in the arms, lower the dumbbell back in an arc motion.
Lower until you feel a stretch in the lats then pull it back to the same arc to be over your chin.
Having an inconsistent bend in the elbows.
Going too far past a strong stretch.
Rushing repetitions.