There have been several books written about the subject of happiness including several from Tal Ben-Shahar ("Happier", "Even Happier" and "Being Happy") and Zappos CEO, Tony Hsieh who wrote Delivering Happiness. All great books if you're looking for a deep dive into the subject of happiness.
But I came across a quote from the Dalai Lama XIV that really nailed it for me:
Happiness is not something ready-made. It comes from your own actions.
Via The Learning Factor