This exercise focuses on dissociation of the scapulae (shoulder blades), it also helps active the core and flute muscles. It will also help you improve your balance since you have to stabilize yourself as you sit and roll on the ball.

Roll down the ball holding a dumbbell. Lie on the ball with the middle portion of your back. Hold the dumbbell next to your chest.
Lift hips into table top, squeeze the glute muscles and engage your abdominal muscles.
Raise your empty hand, so that your arm is extended.
Pull down your empty hand as your raise the dumbbell up extending your arm. The idea is to move each shoulder blade independently from each other.
Alternate pushing and pulling your arms up and down, maintaining the hips high in table top.
Repeat for 10 to 12 repetitions.
Switch the dumbbell to the opposite arm and repeat motion for 10 to 12 repetitions.
Do 2 sets.