Don't Worry, Be Happy!
I consider myself a generally happy person. I mean we all have our moments, but for the most part, I'm content. I like to think that I am "Realistically Optimistic" about life...meaning that while I'm aware of the dour realities of life, I refuse to let them hamper me in anyway. I also have learned to just let go of things that I really have no control over...like the past for example.
I figure that, since I am currently not in the possession of a time machine, the only productive choice I can make is to move forward. And, its this realization that, I think, has had the biggest impact on my happiness...once you stop focusing your energy on the negative and unchangeable, your state of mind completely changes...for the better! :)