When I need to relax, I generally need to do something that doesn't require a lot of brain power, like watching a movie or playing a video game. Usually, when I need to relax, my brain is just over taxed, so I need to do something that means I don't have to think about it too hard so my head can just empty of whatever is buzzing around in there. Crafting, reading, or writing don't work because they still require a lot of thought.
Sitting with the kitties help, too, but only when they feel like staying on your lap.
I also like to take long hot showers.
When I was in school, I would get really jittery around finals. One of the girls mentioned that she would have a glass of wine while she studied because it helped her relax. I tried it the last couple weeks of school because I was so jittery that I couldn't study at all. It does actually help with the jitters, though you need to find the balance between the jitters being gone and your head being foggy, because then you can't study much either. :-p