Some people enter a room of strangers and glide along from one lively conversation to another, uncovering golden new business contacts.

How do they do it?

These people know how to read a room—a capacity that can be partly inborn, but also learned. From the barrage of sights, sounds and behavioral details, they extract clues about which people have the most to offer and which to avoid.

That energetic guy with the 1,000-watt smile, booming voice, ready handshake and a fistful of other people’s business cards might seem like fun, for example. But he’s moving too fast to connect with people in a meaningful way and is probably just trying to bag clients.

“You meet somebody at a business function, and five minutes later they’re slapping you on the back and calling you by a nickname, ‘Yo, Vic!’ Only my close friends call me Vic,” says Vickie J. Gray, chief marketing officer at Ober Kaler, a Baltimore law firm. Such glad-handers “give networking a bad name,” she says.

The cues to finding allies in a crowded room aren’t obvious. Those in groups talking all at once and laughing might look like great people to know. Often, however, they’re sharing a private joke or memories of past experiences, and “they’re having way too much fun” to welcome an outsider, says Anne Baber, co-owner of Contacts Count, a networking consultant from Newtown, Pa., that provides training for attorneys at Ober Kaler.

A tight circle of three to five people standing face-to-face in a closed O, maintaining eye contact and talking intently, might look intriguing, but they may be solving a pressing problem, making them too busy to greet someone new.

The most promising group may be lined up loosely, with gaps between participants, “just sort of muddling along, trying to have a conversation,” Ms. Baber says. They’re likely to welcome a newcomer, especially someone who can loosen them up.

Luiz Vieira networks often in his role as president of a Philadelphia technology and consumer-product materials company and a member of an association of CEOs. He looks for a group that isn’t clicking. “They look like they’re bored, and they need someone to jump-start their conversation,” he says.

Consultant Liz Sears Smith met a new work contact after exhibiting welcoming body language at a museum gala. Photo: Ralph Alswang

Working with Philadelphia impression-management coach Karen Kaufman, he learned to come prepared to talk about a few interesting topics, such as the World Cup or the stock market, and to feel at ease approaching others, asking questions and starting a new discussion. “If you’re able to shift the mood of a group in a positive way, it’s very powerful” in forming bonds with others, he says.

Participants in groups that are welcoming often make eye contact as a newcomer approaches, raise their brows in a welcoming way and smile.

Two people facing outward, instead of directly facing each other, also signal a readiness to talk, says Michele Woodward, a Washington, D.C., executive coach.

Ms. Woodward met Liz Sears Smith a few months ago at a museum gathering after spotting her near a standing cocktail table, leaning against the rail shoulder-to-shoulder with a colleague, looking out at the crowd. “It was clear from their body language that they were open,” Ms. Woodward says. Ms. Woodward and Ms. Smith made eye contact and both smiled. Ms. Woodward introduced herself, and they talked for about five minutes and realized their work was similar in some ways, Ms. Woodward says.

Ways to Behave at a Work Event Do: Come prepared with topics to discuss or experiences to share.

Observe others’ facial expressions and body language in deciding whom to approach.

Look for opportunities to help others with information or introductions.

Keep at least one hand free of snacks and drinks so you can shake hands.

Look for eye contact or a nod from others as a signal to introduce yourself. Don’t: Measure success by the number of business cards you collect.

Look over the shoulder of the person you’re talking to in case someone more interesting shows up.

Try to look smarter and more competent than others so people will be drawn to you.

Assume anyone standing alone is a loser and should be avoided.

Demonstrate your power and influence by talking in a loud voice.

“We decided we wanted to have coffee, and Michele took the first step of sending an email later. We’ve kept that relationship going,” says Ms. Smith, Washington-based reputation-management consultant.

Noticing subtle, nonverbal cues can help. Domineering people tend to talk most of the time and avoid eye contact with listeners, research shows.

People who are genuinely open to new relationships adopt an open stance, shoulders apart and hands at their sides, turning slightly toward newcomers to welcome them, says Kelly Decker, president of Decker Communications, a San Francisco consulting and training firm. Also, their gestures match their words. Saying you’re delighted to meet someone when your arms are crossed in front of you is confusing, suggesting you don’t mean what you say.

Loners who stand in a corner, hunched over their cellphone or a plate of food, are sending a negative signal, Ms. Woodward says. Other singletons, facing the room with an open stance and a smile, however, may be happy to greet you. “For some people, a networking event is the seventh level of hell. If I can reach out and make it a little easier, I’m going to try,” she says.

Influential people often lead the conversation, but good networkers leave plenty of time to show interest in what others say. An influential speaker has listeners who are nodding and leaning forward, raising their eyebrows or murmuring brief responses such as “Really?” or “I see,” research shows. Listeners who stand close signal a desire to please. So do those who mirror a speaker’s gestures, tilting their heads at the same angle or simultaneously shifting their weight onto one foot.

Carl Arnold reads the overall energy level of a room in deciding how to approach people. At a cocktail reception in a restaurant bar three years ago, people were talking loudly, telling stories and laughing boisterously. So he asserted himself by puffing up his chest, standing tall and catching the eye of a man who appeared to be the most influential one there. Mr. Arnold, who chairs leadership groups for Vistage, a San Diego-based executive-coaching organization, introduced himself and made a joke, sparking a lively conversation.

Carl Arnold, center, attended the Vistage Executive Summit in San Francisco, Calif., in May. Photo: Carl Arnold

A recent gathering of musicians he attended was quiet and laid-back, with people talking softly in twos and threes and “sipping a little Chardonnay, as opposed to vodka rocks,” Mr. Arnold says. “I kept it more on the down-low” and sought out the host, who introduced him to others. He met a valuable new business contact at the first gathering and made a new friend, a fellow musician, at the second.

People who try to impress strangers by reciting their résumé are missing the mark, Ms. Decker says. Others are more attracted initially to a person’s warmth, as conveyed by eye contact, a warm expression and a smile, rather than to their competence.

Pamela J. Bradley says networking used to be difficult for her as a shy, introverted person. With training from Ms. Baber’s firm, she says she’s learned to enter the room thinking, “I’m here to help people, with resources or introductions.”

Ms. Bradley, a human-resources manager for Keiter, a Glen Allen, Va., accounting and consulting firm, prepares by thinking up a list of things she can offer in a conversation, such as a tip about a new restaurant, and things she wants to learn. Then, she says, she listens closely to others for opportunities.

Write to Sue Shellenbarger at sue.shellenbarger@wsj.com