Here's what I have actors do at the beginning of a warm-up:
Stand with your legs shoulder-width apart, arms relaxed at your sides.
Let your head drop forward; don't *hold* it down, just let it fall normally.
Slowly "shrug" your shoulders up to your ears, hold them up, let them drop. Do this 4-5 times.
Throughout all of this, be aware of your breathing.
Slowly start to roll your head to one side; keep your chin pointing down. Again, you are not *holding* your head down, gravity is. Allow your head to roll in kind of a 1/2 circle from side to side. This is very slow.
After you've done several 1/2 circles, let your head start going all the way around. As your head tilts back, allow your jaw to fall open. It will do this naturally if you are allowing your jaw to relax.
Do this several times and then allow your head to come to rest in the front again.
Slowly, slowly, begin to roll down, as if you were going to touch your toes. Imagine your spine is curling as you go down. Go down as far as you can without pushing it, stay there for a few breaths, allowing your arms to just hang there. Then, slowly roll back up, as if you were stacking your vertebra on top of each other, with your head coming up last.
Wow - I hope I typed that all out right
I ususally just demonstrate it!