Holding dumbbells in each hand, hinge forward so your back is almost parallel to the ground.
In an arc motion spread your arms out from each other until they're aligned with the shoulders.
Slowly retreat back the same path back to the start position and repeat.
Extending too far past the shoulders.
Not maintaining a consistent arm bend.
Rushing repetitions.
Stand with your feet spaced at shoulder width holding the dumbbells with your palms facing each other. Bend your knees and hinge forward, keeping a straight back.
Start with your arms down with a slight bend then in an arc motion bring your arms outwards until they're aligned with the shoulders, then return through the same path back to the start position. Focus on squeezing your shoulder blades together at the top of the movement. Have a consistent bend in the arms and activate the core to keep a straight back throughout. Repeat for the desired repetitions.
Avoid using excessive momentum from the body or extending too far past the shoulders.
Fitness for all, for life.