Progressive Muscular Relaxation (PMR) is useful for relaxing your body when your muscles are tense. The idea behind PMR is that you tense up a group of muscles so that they are as tightly contracted as possible. Hold them in a state of extreme tension for a few seconds. Then, relax the muscles to their previous state. Finally, consciously relax the muscles even further so that you are as relaxed as possible.
By tensing your muscles first, you will probably find that you are able to relax your muscles more than would be the case if you tried to relax your muscles directly.
Experiment with PMR by forming a fist, and clenching your hand as tight as you can for a few seconds. Then relax your hand to its previous tension, and then consciously relax it again so that it is as loose as possible. You should feel deep relaxation in your hand muscles.