Gratitude seems to be a powerful tool in therapy. It can calm the sleepless, and improve the mood of the depressed, as well as make people make kinder choices. You can find a nice review with some citations here.
Why does gratitude work? My personal hypothesis is that shifting your focus toward noticing what you have, versus what you don’t, puts you in touch with your own personal sense of non-material wealth. Getting into the habit of noticing produces more noticing. It can take the place of worrying about what might happen, what you don’t have, what you haven’t done, etc. Loving what you have and tending it, seems to make it grow. Brief gratitude exercises, like those currently filling social media sites like Facebook, can actually help. I have offered these exercises to some of my clients and they find them helpful in redirecting their attention from whatever they are worrying about, to what they have. Here’s one exercise: at the end of each day, take five minutes to name (or write) the things for which you are grateful. For example, right now I am hearing the sounds of heavy construction two houses away from me. I might say “I am grateful for the fact that I can hear”. I could add “despite the fact that I am listening to construction noise”, but that would defeat the purpose. In fact, it is true that I am happy I can hear and noticing that helps me tolerate the “noise” factor, because in noticing that I can hear, I can also hear the birds. So, in the exercise there are no “but”s allowed. The gratitude can be for small or large things, but they must be genuine and belong to the person’s value system. The investment for this kind of practice is small, but the effect can be quite powerful.