Taking a break when you get hot is key. It's hard to do that in a tourney or SNG though. Psychologically, if I get the worst end of a bad beat, I really try to make a point of laughing it off and typing in NH or GG in the chat box, instead of calling the guy a donk, idiot, or questioning how they can play cheese like J2 offsuit in early position. It sounds too simple, but I find that helps interrupt the rage/anger response a bit... laughter does block some of the stress hormones your body releases.
I also remind myself right away of times I've sucked out as a dog in a hand, which everyone does more often than they might like to think. Obviously you want to be in a position to suck out less often than a fish, but everybody still sucks out pretty regularly. Remind yourself it all comes back around, and if you are the better player, the good will come back around your way more often than not... even if it takes awhile to see those results. Of course, if you are tilting off your chips, the reverse will be true... so remind yourself also that a stupid play made in anger will cost you both immediately and over the long run.