It depends on what the situation is, but I usually just grab my journal and start writing furiously about anything and everything. I've already filled up one of those composition books in just 7 months and working on my second. And that's only because I had some time jumps. Anyways...
Writing is good for me, like it gets all my frustrations out of my head. Writing poems takes more effort, but worth it if that's your thing.
And this probably sounds strange, but crying really helps. I was really upset last year and needed a good cry, so I stuck Bicentennial Man into the DVD player, grabbed a box of tissues, and watched it. (great movie- just has some amazing sad moments for me)
I dunno what to say, really. I have slight ADD or something, because I'm always doing something with my hands, like typing or writing or anything..oh, and music is good too. I've found it very calming.