Martin Seligman who is considered the father of positive psychology suggests guidelines for how to write a gratitude letter

Write a letter on one page of paper and have it laminated.

1. Take up to a month if necessary to comprise the letter. Carefully consider all the ways this person has contributed to your life.
2. Then, make an appointment with this person without letting them know what the visit is for.
3. Invite them to your home, or visit them at their home.
4. Then, spend this time together sharing with this special person all of the things about them that you treasure.
5. In times of the pandemic, you could do this virtually, and surprise them with a screen share, text of the letter, picture of it.

For those who are too intimidated by the prospect of staging a gratitude visit, to share your letter writing a gratitude letter, and sending it, ( or even just writing it in your journal without sending it) also has
tremendous benefits. You can write a series of letters over a course of time to people who have made an impact in your life, some you know well or, even  some you do not know so well. Or, you could write just one letter to
someone to see if you enjoy or benefit from the experience. You could start with whomever you are most comfortable with: your  sister or cousin, a mentor from earlier on in your life, and just express the impact they have
made on you and thank them! You could even write a letter to someone you don’t know personally such as a writer who you appreciate or an artist, or even the cashier in the local grocery store who is friendly to you every week.
Think of all the ways they have made your life and the lives of others around you easier and express your gratitude and thanks for them!

Questions to ask yourself if this is a person who made an impact on your life in the past.

• What might your life be like if I had never met this person?
• What lessons did this person teach me?
• How did I become a better or wiser person?

Questions to ask yourself if this is a person currently in your life.

Imagine this person was gone.

• How would I be impacted? What would I miss?
• What do they bring to my life?
• Do I tell them enough of the importance they have to me? Do I appreciate them and value the things they do/have done  for me?

Questions to ask if this is a stranger 

• What does this person do that ads value to my life?
• How to they help me to function?
• What must their daily life be like?
• How many other people do they impact?
• Are they valued the way they should be by society?

People to write letters of gratitude to:

You may also think about writing letters or making visits to people who impact the lives of people you love. For example your parents, children, friends or spouses. How have these people cared for or impacted the lives of your loved
ones?

You may think of someone who made an impact on you only once. For example, a person who made a difference in your life when you were vulnerable or lost, in crisis or need, and you remember a kind act that made an impression on you.
Gratitude letters can be written to principals, therapists, or doctors who have helped you in times of need.