Increases in the sense of free choice better predict increases in happiness than do increases in income, democratization, social tolerance, and lots of other stuff not on this chart.

FORBES: Happiness, Freedom, and Autonomy

That physical display of how you're feeling - for example, if you're feeling happy, the physical display of happiness on your face and, perhaps even in your gestures, increases the feeling of happiness, just as the physical display of sadness increases your feelings of sadness.

NPR: Can Botox Treat Depression Along with Wrinkles?

Together they sweep up a host of studies which suggest that marriage increases health and happiness for both sexes.

ECONOMIST: I do, I can, I will