one of the best stress relief techniques is to start at your feet, and tense the muscles in each part of your body, working up. you can let go of them right after you tense them, or you can wait until your body is all tense, and then release your muscles all at once (i think the latter works best). it relieves stress and relaxes muscles.
also, if you're up to doing a bit of yoga, that would probably help a lot. it's very calming for the body and mind, and it's pretty fun if you put on some good music to stretch to. yoga's better than just stretching randomly, because it works certain muscles in certain ways and is more fun. you'll keep your muscles relaxed if you have a bit of yoga in your day. (i do a 1-hour yoga routine every day, and it's fun~)
as for other stress relief exercises, here's some:
breath in deeply, breathe out. try to clear your mind and just imagine the air going in and out of your lungs and all through your body. do this for a while, trying not to think of anything else.
try visualizing that you are somewhere else, somewhere nice. imagine how each of your senses would react to that environment. try to smell, see, taste, etc. everything you are imagining. this one is good for doctor visits and things, especially if you're a bit drugged up and numbed. xD (works well for me~)
so yeah, dunno if any of those are what you're looking for, but i hope it helps.