I have studied gratitude for more than two decades, and one common theme emerges repeatedly: Even basic expressions of thanks have remarkably powerful effects. Knowing that others—whether managers, co-workers or clients—appreciate our actions makes us feel valued. And when you feel valued by someone, you think more highly of them and are more willing to go out of your way to help them.

But while showing gratitude isn’t difficult, how to do it well isn’t always obvious. And the nuances can make all the difference.

Here are a few guidelines drawn from my research.

A little thanks goes a long way

For many daily events in the workplace, it may not even cross one’s mind to express gratitude to a colleague. So many tasks happen within a day that it may hardly seem worth it to stop and say thanks.

That’s a missed opportunity. The fact is that all it takes is some acknowledgment of another person’s work—a brief email, Slack message or passing comment in the hallway—to see beneficial effects. My research team and others have found that people who express their gratitude are seen as warmer, more competent and more caring about others—and the people being thanked actually do extra work for them.

In one experiment, participants were asked to edit a cover letter. Some were thanked by the person they helped, and some weren’t. After that, the participants were asked to edit a second letter. The ones who had been thanked devoted an average of 15% more time to the task than those who hadn’t been thanked—23 minutes, compared with 20.

The reason they worked harder is the most important part of the story: They felt valued, which helps build a high-quality relationship with the person who values you. High-quality relationships are the ones that we give priority to, that keep us energized, that we rely on when things are challenging. And they are the ones for which we are willing to make sacrifices.

This positive effect even applies to observers: If people simply see someone thank another person, they are more inclined to help that grateful person.

In one series of experiments, we asked participants to help a writer prepare a document. As part of their instructions, participants viewed, as an example, a document that a previous reader had worked on, including tracked changes where the previous reader had corrected some typos. This example document also included several comments from the person who originally wrote it. In some cases, the writer expressed gratitude to the previous reader by adding just one extra comment that read, “Thank you so much for catching those typos!” In other cases, the writer didn’t leave any thanks.

Participants whose example document had a simple thank-you to the previous reader were then more likely to go above and beyond to help the writer on the new document they were helping with: About 38% of those participants corrected typos they found—even though fixing typos wasn’t part of their assignment.

The effects of gratitude aren’t just psychological. In one recent study, we asked pairs of teammates to put together a pitch for a new project, under tight time pressure. We found that when one person showed the other gratitude before the task, on average both of them showed an improved cardiovascular response that may leave them better prepared to handle the job.

Specifically, we assessed the teammates’ heart function and blood pressure to compute a measure of cardiovascular efficiency—in essence, an index of whether we see a task as threatening, as opposed to challenging. Teams, where someone expressed gratitude, showed no cardiovascular threat response during the stressful task. Teams without expressions of gratitude showed a significant threat response during the task.

All too often, when we thank someone for helping us, we focus on ourselves. We might say, for instance, “Thank you so much for covering that meeting for me—I am so relieved I didn’t have to do it!”

But it is much more effective to focus on the other person’s contributions: “Thank you so much for covering that meeting for me—you really went above and beyond by jumping in at the last minute!”

It isn’t bad to say that you were happy or relieved, but focusing on the other person makes them feel more valued. All our evidence suggests this is the active ingredient in why gratitude expressions make a difference for the people who hear them. We call it “putting the ‘you’ in ‘thank you.’” (A phrase coined by my friend and colleague, Barbara Fredrickson—thank you, Barb!)

This emphasis can even affect observers. We conducted experiments where participants watched videos of real people thanking each other for real acts of kindness. The videos varied in how much the people focused on their benefactor’s positive actions when expressing gratitude. None of the participants knew the people in the videos.

When the video thank-you messages focused more on the benefactor’s actions, participants watching the videos said they were more interested in getting to know the grateful person and were more willing to help them “if they were in a crisis, even though you would have to go out of your way to do so.”

Be real

In our studies, we ask people—whether it’s the person being thanked or someone observing the thank-you—how genuine the grateful person seems. Do they seem to truly understand, validate and care about the person they’re thanking?

It’s a vital question. One study looked at the relationships between people who were thanked and the grateful people who thanked them. How would their relationship be affected if the person being thanked thought the grateful person was showing true care and concern, that the grateful person really valued them? The results showed this perception of the grateful person was statistically associated with greater satisfaction with the relationship six months after the expression of gratitude.

Likewise, this perception of the grateful person’s care, understanding and valuing of their benefactor is what drives observers to be more interested in getting to know and willing to help a grateful person they have never even met.

These findings suggest that the heart of when and why gratitude works is when it is genuine. So, there isn’t any need for people to pretend to feel more gratitude than they actually do, or to pretend the other person was more amazing than they actually were.

Instead, when people want to show gratitude, I encourage them to express it when they feel it and focus on specific things that the other person did. Perhaps the person completed a task early, or in a particularly creative way. Or maybe they took a junior colleague under their wing. By staying specific about what you found particularly great or noteworthy about the person’s actions, it is easier to make them feel valued, and there’s little risk of going over the top with thanks. Gratitude grounded in reality is the best way to make a person feel valued.

Give thanks publicly

In some cases, expressions of gratitude can be even more effective when they are made publicly. Demonstrations of gratitude in group emails, Slack messages or in-person meetings send at least two important signals: First, people learn that the grateful person notices and acknowledges others’ contributions, and that is appealing. Second, people learn that the person being thanked is generous, and they’re interested in getting to know and willing to help out that person.

In short, by expressing gratitude in a public way, you may do even more to give back to the person you’re thanking.

In one experiment, participants watched a video of a stranger who used a webcam to record a message to someone else (who wasn’t seen in the video)—sometimes this was an expression of gratitude, sometimes not. We asked participants to rate their interest in getting to know both people—“I would enjoy spending time with the person” and “I can see myself being friends with the person,” for instance—on a scale of 0 (not at all true) to 6 (very true).

Participants were fairly interested in getting to know the strangers, generally delivering ratings above 3 in all instances. But they were significantly more interested in getting to know the people in videos where gratitude was expressed—not only the grateful person, but also the person being thanked. For example, in cases where gratitude wasn’t expressed, participants rated their interest in meeting the unseen person at 3.77. In cases where gratitude was expressed, that figure rose to 4.60.

We are still testing how far this goes. Are there downsides to public gratitude? Might other team members get jealous? But we see this as a promising avenue for even more efficiently building connections among community members. These connections, in which people feel valued and seen by one another, are what help keep us engaged, enthusiastic and willing to help when the going gets tough.

Dr. Algoe is a professor at the University of North Carolina at Chapel Hill’s department of psychology and neuroscience, and founder and director of the Love Consortium. She can be reached at reports@wsj.com.