Effective PAIs used in the study included writing letters of 
gratitude, counting one's blessings, practicing optimism, performing 
acts of kindness, meditating on positive feelings toward others, and 
using one's signature strengths, all of which can be easily 
implemented into a daily routine at low cost.

http://www.medicalnewstoday.com/releases/232017.php

www.peoplewho.org