If you are looking to make someone — even yourself — feel better during what has been a hard winter of the pandemic, consider writing a gratitude letter. You can think of it as a slightly longer and more meaningful thank you note, but instead of offering thanks for a physical gift, you are offering thanks for something that was done or said.

There are two excellent reasons for writing a gratitude letter: It will make you feel really good, and it will make the recipient feel great. Among the research showing the benefits of letter writing is a study led by Indiana University and published in 2016 in the journal Psychotherapy Research and led by Indiana University, which tested whether gratitude writing helps people seeking psychotherapy. Scientists randomly assigned the 293 participants to three groups: Those receiving psychotherapy, those receiving psychotherapy and participating in expressive writing, or those receiving psychotherapy and participating in gratitude-letter writing. Even in the small study, participants in the gratitude group reported significantly better mental health than the other two groups, even three months after the trial ended.

On the receiving end, opening a gratitude letter feels even better than you might imagine. Amit Kumar, a social scientist at the University of Texas at Austin, studies the reactions of gratitude-letter recipients.

“It’s not like it makes some people feel great and some people feel just OK and some people feel kind of weird,” he said of his research findings. “Almost everybody is saying that they feel really, really great.”

The main barrier to expressing gratitude in a sentimental letter, he said, is the perceived awkwardness. “Part of the reason we did this research — the hope, at least — is that we will encourage people to do this more often,” Mr. Kumar said. “If you know from empirical research that it’s not actually as awkward as you think, and that it will mean a great deal to the person, maybe that can help you get over that hurdle.”

So if you were waiting for the right moment to start fully expressing your love and gratitude, perhaps that time is now. Here’s how to start.

Determine the recipient.

The first step is to decide whom to write to — perhaps a career mentor, a supportive family member or a dear friend.

When Chris Schembra, author of the book “Gratitude and Pasta: The Secret Sauce for Human Connection,” runs virtual gratitude workshops for executives through his company, 7:47, he begins with this question: “If you could give credit or thanks to one person in your life that you don’t give enough credit or thanks to, who would that be?” The answers vary, he said; executives have mentioned a former boss, a fifth-grade teacher and a stranger who saved a life.

Nancy Davis Kho, who in 2019 published “The Thank-You Project,” a book about her year writing 50 gratitude letters, offers this exercise: “Quickly, think of the five people you want to hug first after quarantine.” Then write their names down, she said, because “even carrying around that list is a reminder that you are not by yourself.”

Gather your supplies.

Decide your letter-writing method and get your supplies, such as stationery or notecards.

Handwritten letters are the gold standard because your handwriting is an extension of you. It’s personal and tactile. And don’t let messy penmanship be a deterrent: No one is expecting calligraphy. But there’s nothing wrong with typed letters; Ms. Davis Kho prefers to type and then print hers. Either way, the point is to create a physical artifact that the person first enjoys as a surprise in the mailbox, and then can keep as a memento.

Think about your recipient.

Once you have decided whom to write to, think about that person and his or her role in your life. You don’t need to spend a lot of time, but clear away any distractions and focus on some of your most cherished memories of this person. Think about how you met, what the recipient has done for you at what cost, what the person said that you have never forgotten or ways you have applied his or her advice in your life. Jot down a few bullet points or even a short outline if you would like, but do not overthink or get caught up on planning. A gratitude letter need not encapsulate your entire relationship, or cover everything this person means to you. You can say thanks for just one thing.

Sit down and write.

If it makes you more comfortable, you can start the letter by detailing a reason for reaching out. Ms. Davis Kho started her letters by explaining that it was a milestone birthday year for her, and that she was writing to people who had made a difference in her life. You could say you were inspired by this article. Or, you can keep your letter-writing reasons to yourself and just start with “thank you.”

Think back to your brainstorm, and, using evocative details, tell the person why you are grateful. That could be the exact words you remember this person saying, and where you were when they were said. Add how it made you feel — then and now. The recipient might remember the event or favor you are referring to, but the person most likely does not know how it made you feel (Thankful, probably, but also, perhaps, joyful? Safe? Relieved? Inspired?) Don’t hold back. It takes a little bravery, but writing sincerely and from the heart turns a polite note into a meaningful memento.

Write in your style.

Don’t worry about crafting each sentence just so. You’re trying to get to the meaning behind the words. If you can, try to write the way you speak. Imagine the person is on the phone: What would you say?

You might get caught up in selecting exactly what to say. But Mr. Kumar suggested you remember that your recipient will not be scrutinizing your choice of words.

“They are just reading what you have to say, and thinking, ‘This is really nice,’” he said. “They aren’t thinking, ‘Well, how could it have been nicer?’”

Instead of writing a traditional letter, feel free to write a more casual bulleted list. To a career mentor you might say something like: “I’ve been looking back on the stages of my career and thinking of people who made an impact. You are high up on the list. Here are five times your advice made a difference.”

Finish strong.

End with gratitude, and a compliment. What does this favor or event say about the person? Is it indicative of her or his generosity or kindness? Say that explicitly. With the final “thank you,” you could perhaps add a wish for the future — to meet at that museum you both love, or to return to the town where you met.

Keep copies.

Just as your recipient might keep the letter, so can you. Snap a picture or scan the letter before sending. Ms. Davis Kho has printed out all of her typewritten letters and bound them into a book. “When I’m feeling low, the book reminds me that I’ve done a good job selecting people,” she said, “and that there are people hidden in plain sight who make our lives better.”