Gratitude is a very powerful mechanism for letting go of stress in your life and regaining your happiness. Here is a very simple exercise from the Positive Psychology Center at the UPenn in the article A very different kind of upper:
At the end of each day, take a moment to go over three good things that happened to you. Think about why they happened and what you did to make them happen.
You don’t even need to have a good pick-up line.