James Altucher writes, "I wasn't grateful for what I had. Else I would’ve treated these ephemeral things (money, love, health, happiness) with better respect and worked harder to hold onto them."

He then goes on to explain how to have an attitude of gratitude.

Great read: http://www.jamesaltucher.com/2011/10/how-to-use-gratitude-to-get-rich/

I also love this piece of advice from that article:

Try this: every day write 5 emails to people you are thankful for.

Or you might want to write the thank you's on paper and hand deliver them.

Doing that is one of the few scientifically proven methods for dramatically increasing happiness in the short term.