Breathe....and always think before speaking...
Its OK to speak, just take a few seconds and think before you respond. Try not to provide an emotional response thereby sinking to their level, and likely being drawn in to what they want.
Sometimes walking away from a tense environment can help to clear your mind. Also writing down your feelings is another way to release emotions.
Its really works for me too. I feel a sense of relief. But sometimes old feelings do creep up, and I do feel upset again. I guess its about finding a balance. Its healthy to be upset about things, but its gets unhealthy when it overrides your life and your constantly feeling down. Anyway, wishing you all the best.
Make urself busy and do things u like dress ur self up, eat ur favourite food :D
Find something that makes you happy. Personally I like to write Diaries, poetry, short stories to get my mind of the things that get me down, or if I've just had a bad day Music is a great way to get a boost of happiness.
ask yourself, "is this situation worth getting myself upset about? it is really worth all my effort?"
Practicing a good meditation technique should do it, in my not-so-humble opinion.