Smile more often

Force yourself to smile. Try it; it's not that difficult. Now hold it for a count of ten and deepen it. Mentally affirm, "I am happy, totally, blissfully happy." Notice how your mood begins to shift. You can't help but feel a little lighter. Use your smile to start a happiness epidemic. Smile at everyone, everywhere. People are hardwired to respond to facial expressions they encounter. If your glower at someone, that person will return a frown, but your smile will evoke a smile. You'll feel happier too, because your body responds to your smile, even if you're faking the grin. So fake it until you genuinely feel happy. Once you know it works, do it often!

Taken from: "365 ways to life happy" by Meera Lester