Counting your blessings for what you have (either to a close other or privately, through contemplation or a journal) or conveying your gratitude and appreciation to one or more individuals whom you have never properly thanked.
The happiness strategy "Expressing Gratitude" is one of 12 scientifically proven ways to increase your happiness level. It has many facets. The following figure lists 2 of the most important ones.
Facets of Strategy