Great summary:

There’s an overwhelming amount of happiness research.

Forget incorporating it all into your life — merely remembering it is daunting enough.

I like to keep it simple: Remember the 4 P’s.

1. Purpose
2. Perspective
3. People
4. Play

Work those into every day and you’ll be smiling more.

Eric's article has details: http://time.com/95960/the-way-to-happiness-remember-the-4-ps/

Also worth reading:

http://pandawhale.com/post/23824/why-cant-we-predict-life-satisfaction-over-the-life-cycle-people-are-bad-at-predicting-what-will-make-us-happy