This is a simple technique from Yoga. It works on a simple principle: If you tense muscles and then relax them, they are always more relaxed after you have just tensed them.
First, make your hands into tight fists... as tight as possible.
Notice the tension in the muscles of the fingers. Become aware of the hardness of your fingernails in the palm of your hands. Notice the skin stretched across the knuckles and how your wrists have become rigid.
In a moment... begin to relax your hands.
When you do... really concentrate on the change between tension and relaxation.
The relaxed feeling is now going up your arms to your shoulders. In a few minutes it will spread to your whole body.
You don't have to say anything or do anything. Let the relaxation flow.