(This is one of my top five favorite tips.)
Maintain some privacy.
Don't share every gruesome detail of every single thing that bugs you. You don't have to tell anyone that you're having a bad hair day, that your dinner last night was a little overdone or that your significant other farted so much in their sleep that you need to repaint the bedroom. You don't need to tell anyone about the most recent spat with your spouse, or how someone cut you off in traffic.
Sometimes, talking about those things gives them an importance they don't really merit. Your friends will probably comfort or commiserate, and then tell you their latest tale of woe. The next thing you know, the whole world seems gray.
So keep the minor mishaps of daily life a private matter. Tell yourself they aren't important enough to think about anymore, let alone share with someone else. You'll see it makes a difference in how important those mishaps seems to be.