An awesome video on gratefulness! Another version is this video which has video clips instead of static photos; audio narration is the same.
Kelly McGonigal is Professor of Psychology at Stanford. Her sister Jane McGonigal is a game designer. In the video above, they outline a technique for thankfulness: identify a person, their action (for which you're grateful) and a quality in that person. Then express thankfulness in the form of a note which mentions their action and their quality.