Just like the other neck stretch you can do this stretch either sitting or standing, but again I would recommend doing it sitting down. Why? - because just like the other neck stretch, if you stretch standing up your body's reflexes will activate to prevent you from over balancing and this will in turn reduce the effectiveness of your stretch.
Sit tall - elongate your spine, hold your head up and don't slouch or hunch your shoulders.
Interlock your hands and place them on your forehead. Take a deep breath in, then as you exhale lighty pull your head backwards as if looking to the sky directly above you. You should feel stretching tension through the front of your neck down to your collar bones (or Clavicles).
Hold this position for 15-20 seconds, and don't hold your breath, then gently release the tension.
Try to keep your neck long as it extends over your shoulders - that is don't let it slouch or collapse on itself. Imagine you are leaning your head over a pipe or some other structure that is placed immediately behind your neck and shoulders.
Try not to hunch your shoulders up as you stretch. Some of the muscles you are stretching attache to your clavicles and 1st/2nd ribs, and if you hunch up your shoulders it will lessen the effectiveness of your stretch. Just like with the other neck stretch, mentally try to stabilise your shoulders and lock them down to maximise your reward for effort.
Try not to pull too hard - only to the point of tension in the muscles of the front of your neck. Don't forget there are delicate structures that run through your throat - especially your airway! Don't restrict your oxygen by over stretching your neck.
Variation to include some rotation:
The stretch as outlined above will stretch both sides of your neck simultaneously - that is left & right, not front & back by the way. As you become more comfortable with this stretch you can progress to this variation that includes some slight rotation to target each side individually, and reap a greater stretch for your efforts.
Use the same starting position as for the original stretch, then place your right hand on your forhead with the fingers slightly more on the left to give better control. Prepare exactly the same as before - elongate your neck, stabilise your shoulders, deep breath in. This time when you exhale, gently pull it to the right and back, as if trying to put your ear just behind your shoulder ... follow me? Hold this for 15-20 seconds, continuing to breath, then gently release and repeat on the other side. Remember that it takes 1 stretch on both sides of this variation to equal just 1 of the original version of this stretch - don't leave yourself unbalanced!
Always remember to relax into your stretches - don't fight against the stretch (it may cause more harm than good), and always do each stretch 3 times, at least twice each day.
Taken from "Stretching Anatomy" by A.G.Nelson and J.Kokkonen - pp 4-5