HOW: Sit up straight and grab hold of the edge of the chair. With the other hand, pull you head diagonally forward to stretch the back/side of the neck. Hold the stretch for about 10 seconds and repeat a few times on both sides.
This is great if you have a stiff neck after a long day at the office. You can of course do this stretch exercise in many other places as well eg. when on the toilet, in a meeting, etc etc.