Do something based on science, not on some kooky self-help guru.
The scientific literature supports only a few interventions that can measurably improve happiness:
- keeping a daily gratitude journal (in which you write down what your thankful for at the end of every day; there's a great iPhone App for this actually)
- giving things to others
- investing your resources in experiences versus materials (a new gadget eventually loses its shine, but fun experiences, especially with friends, improve happiness over the long-term)
- join a group that meets regularly (regardless of what kind of group it is); there's actually really strong evidence that this measurably improves happiness