Sit on a bench and lie on your back, holding a Dumbbell with both hands above your chest.
Slowly bring your arms overhead and let the weight open your shoulders at the bottom.
Take care to keep your Abs engaged and your lower back in contact with the bench.
Bring the weight back up above your chest.
Form tips
Do not let your lower back arch, especially when lowering the weight down, as that would decrease the angle at the shoulders and make the exercise less beneficial and your progress harder to track.