Performing the: A Step-by-Step Tutorial Dumbbell One Arm Bench Fly
Extend the arm holding the dumbbell straight up towards the ceiling, keeping a slight bend in your elbow to avoid strain.
Slowly lower the dumbbell in a wide arc until it is level with your chest, keeping your arm slightly bent at the elbow throughout the movement.
Pause for a moment at the bottom of the movement, then use your chest and shoulder muscles to reverse the motion and raise the dumbbell back to the starting position.
Repeat this for the desired number of repetitions, then switch to the other arm and perform the same steps.