This is not a new concept.  You've heard of Oprah Winfrey? Gratitude journaling is one of the things she attributes to her success.  At the end of the day, she writes down 5 things that happened that day that she is grateful for that was unique to that day.  But you need to do more than just write grateful things down.  You experience them on an emotional level, facilitating the neuroplastic changes necessary to experience those sensations again and again.

The two times of day that have the greatest impact on how that day is going to unfold for you are the 20 minutes before you fall asleep and the 20 minutes after you wake.  End your day on a positive note, journal thoughts of gratitude.