I take a walk, if I can - anything that can get me out in nature.
I feel like I'm never calmer than when I'm working on a piece of artwork or jewelry... or when I'm fishing. Just tossing a lure back and forth into the waters of my local creek, or working a fly is just very peace-making for me. Again, it's an out in nature thing, but there's also something about a repetative, yet potentially productive activity that does that for me (actually catching fish is a big bonus).
Also, once, when I was really angry and upset about something, I tried something that sounds very weird that I learned from people in the psychology profession: Chucking ice cubes into a bathtub. I'm serious! It helped just a little. There's something about throwing the ice cube violently into the tub and hearing them clink and crash that can "get out anger" in a way that doesn't hurt anyone.
But, mostly, for me, it's art and nature that helps me. A couple of years ago, I was undergoing some very bad things and... I think fishing might have saved my life.