Eric Barker offers a nice and simple idea about being happy. In turn, he got it from Dan Pink, who writes a lot about being motivated (and happy).
First, what happiness is not. It is not about having nothing to do - or free. That produces boredom, which is stressful. To the contrary, we feel happier when we are busy but have no time pressure or stress.
The cool thing is that in our personal lives, this is something we can control. We can control what goals we set for the day (that challenge us and keep us busy). It is at the core of gaming as a life style.