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.
Lie on a flat bench, holding a dumbbell in each hand with your arms extended over your shoulders and knuckles pointing upwards.
Start by bending your elbows, lowering the dumbbells towards your ears until your forearms are approximately parallel to the ground. Then slowly extend the elbows back to the start position. Keep your elbows in a constant position throughout the movement. Repeat for the desired repetitions.
Avoid allowing the elbows to move around too much.