Seated in a chair with good posture, hold a ball with both hands close to the body, with elbows bent and pulled in close to the ribcage.
Slowly rotate your torso to the right as far as you comfortably can, being sure to keep the rest of your body still stable. Rotate back to the center and repeat in the oppostie direction. Do this 8 times, with two twists counting as a full set.
Rest. Do another 8 sets (two twists each).
Modification: A ball is not required for this exercise. Imagine you are holding a ball while performing the motion, or hold a small object such as a can of soup or water bottle to add resistance.