Berkeley University explains how, and why to do this as well as evidence and sources that it works.
The better part of one day
HOW TO DO IT
This exercise is best completed on a day (or two) when you have a lot of free time, such as on a weekend. Step two may require some advanced planning with others. In the morning when you first wake up, review the following instructions and make a plan for the day.”
This is a great find. These short 4 steps will make a difference in your life. Here’s the basic premise. We can mindfully consciously create positive life enriching experiences and then practice recalling them. First choose some activity you enjoy doing by yourself and make time to do it today. Next select some activity you enjoy doing with others and set aside time to do that with someone. Perhaps you might go for a walk with someone or meet for coffee for example. Then select an activity you find to be very important and personally meaningful like spending time with your spouse or kids, writing in your journal or going to a place of worship. Then after you’ve done these each of these types of activities at the end of each day sit in a quiet relaxed setting and remember how you felt during that activity. Remember how you felt and what happened during the activity and allow yourself to experience it again in your mind’s eye. This practice of purposeful good actions and recall will create a reservoir or bank of good memories and strengthen your mind’s ability to recall the good.