Keep the arms straight the whole time and resist the temptation to bend at the elbows: this exercise helps dissociating scapular movement from elbow movement.
Slowly push your shoulders forward (protraction), downward (depression), backward (retraction), and upward (elevation) in a controlled circular motion.
Go slowly and take the time to go to the full range of motion in each quadrant.
Keep your Abs tight and a posterior Pelvic tilt : the body forms a straight line from shoulders to feet.