Making a great first impression is supposed to be fairly simple. Smile. Make eye contact. Listen more than you speak. Ask questions about the other person.

And, oddly enough, simply believe you will make a good first impression. A 2009 study published in Personality and Social Psychology Bulletin shows people who expect to be “accepted” act more warmly and therefore are seen as more likable. (Of course you genuinely have to believe you will be accepted — or at least “George Costanza believe” you will be accepted — which is obviously the hard part.)

So, yeah: You know what to do. But knowing what to do is never a guarantee of success.

How can you tell if you actually made a good first impression? Science to the rescue.

According to a 2018 meta-analysis of more than 50 different studies published in Psychological Bulletin, the key is to look for specific nonverbal and verbal signs to determine if you’ve established some degree of rapport.

1. Smiling and laughing. No surprise there. But most people reflexively smile back, especially at first. And then there’s the Jimmy Fallon-esque “Oh, my gosh, I’ve never heard anyone say anything so funny” kind of laughter that doesn’t indicate anything genuine.
2. Holding eye contact. Also unsurprising; the eyes are usually the first indication the other person is thinking about somewhere they would rather be.
3. Maintaining physical proximity. We all define “personal space” differently; the fact you back up half a step might just only mean I’ve slightly encroached on yours. Yet according to the researchers, physical proximity is a key indicator of likability.
4. Starting new topics of conversation. Another less obvious, yet important, indicator. If there’s no spark, polite people will see the current topic through and try to move on. But if they bring up something else, without prompting…
5. Unconsciously mimicking nonverbal expressions. A 2019 study published in Cognition and Emotion shows that when other people mimic your nonverbal expressions, that indicates they understand the emotions you’re experiencing — and may even result in “emotional contagion.” (Which means, if you want to use your first impression skills manipulatively, copying the other person’s expressions and gestures can make you seem more likable.)

So: Imagine you meet someone new. You know what to do. Smile. Make and hold eye contact. Laugh when appropriate. Don’t back away. Shift the conversational focus to the person you just met; one way is to use the 3 Questions Rule.

All the while, pay attention to how the other person responds. Whether they smile, laugh, and hold eye contact.

And more important, whether they maintain physical proximity, initiate new topics of conversation on their own, and mimic some of your nonverbal expressions.

And then use what you learn to make a better first impression with the next person you meet.

Because the next person you meet could turn out to be one of your most important connections. Or one of your biggest customers.