Text from the following online course offered by EdX website.
BerkeleyX: GG101x The Science of Happiness
Happiness Practice #1: Three Good Things
This exercise asks you to remember and list three positive things that have happened in your day so far and consider what caused them.
10 minutes/day for at least one week.
Each day for at least one week, write down three things that went well for you that day, and provide an explanation for why they went well. It is important to create a physical record of your items by writing them down; it is not enough simply to do this exercise in your head. The items can be relatively small in importance (e.g., “my co-worker made the coffee today”) or relatively large (e.g., “I earned a big promotion”). To make this exercise part of your daily routine, some find that writing before bed is helpful.
As you write, follow these instructions:
Give the event a title (e.g., “co-worker complimented my work on a project”)
Write down exactly what happened in as much detail as possible, including what you did or said and, if others were involved, what they did or said.
Include how this event made you feel at the time and how this event made you feel later (including now, as you remember it).
Explain what you think caused this event—why it came to pass.
Use whatever writing style you please, and do not worry about perfect grammar and spelling. Use as much detail as you'd like.
If you find yourself focusing on negative feelings, refocus your mind on the good event and the positive feelings that came with it. This can take effort but gets easier with practice and can make a real difference in how you feel.
Visitors to a website received instructions for performing this exercise and four others. Writing about three good things increased happiness for each time point during a six-month period (immediately afterward and one week, one month, three months, and six months later).
Why it works
By giving you the space to focus on the positive, this practice teaches you to notice, remember, and savor the better things in life. It may prompt you to pay closer attention to positive events down the road and engage in them more fully—both in the moment and later on, when you can reminisce and share these experiences with others. Reflecting on the cause of the event may help attune you to the deeper sources of goodness in your life.