Smile! A videoconference camera may be aimed at you.

Thanks to better, cheaper technology, more Americans now conduct business -- ranging from global brainstorming meetings to screening interviews with search firms -- via videoconferencing. That means your video performance could help or hurt your career.

Videoconferences represent "a great tool for far-flung managers to gain additional exposure and make a name for themselves back at corporate headquarters," says Jeffrey Schwartz, chief executive of ProLogis, an industrial real-estate investment trust in Denver, Colo. More than 25% of the REIT's 900 employees world-wide regularly take part in videoconferences, compared with fewer than 5% five years ago. Mr. Schwartz says his one or two videoconferences a week make him "a better leader."

On the other hand, you risk making a fool of yourself if you forget that associates glued to screens in five countries can watch you twirl your hair, pick your nose, bite your lip, check your BlackBerry or scratch an armpit. "The camera magnifies and exaggerates everything," notes Peggy Klaus, a communication coach in Berkeley, Calif. You must be on your best behavior from "the moment you put your toe in that room" with the video camera.

To improve your chances of shining on camera, I gathered videoconferencing etiquette tips from coaches, recruiters and frequent corporate users. Here are their best dos and don'ts:

• Choose what you wear carefully.

Adam Bauman, head of STI, a New York talent-management firm, often counsels executives at their homes via videoconferencing. Some don a shirt, tie and shorts for the sessions because they expect the screen to display only their upper torso. Then, he reports, they stand up to fetch something and get flummoxed because they've been caught wearing casual attire below the waist.

Mr. Bauman urges executive clients to dress well top to bottom for videoconferences with recruiters -- and to refrain from wearing busy patterns during any video meeting.

• Speak in crisp, conversational tones and pay close attention.

When you want to sell an idea, it helps to lean a bit toward the camera. Women will do better if they perch on the edge of their seats throughout the session. Otherwise, "they look invisible," says Teri Cavanagh, president of TLC Connections, a Pocasset, Mass., concern that offers advice on marketing to women.

• Both genders should maintain eye contact with remote viewers and live participants. You appear stiff if you stare at the screen constantly.

But don't overcompensate. Distant watchers will notice if you gaze away frequently or seem detached for other reasons. "Be careful not to frown, slouch, put your chin in your hands or bob in the conference chair," says Lynthia Romney, president of RomneyCom, a public-relations firm in Westchester, N.Y.

She recently facilitated a videoconference for a U.S. professional-services client involving 13 people in New York and London. Several felt irritated when two U.K. attendees left the room and a third leaned back in his chair. Ms. Romney finds such behavior "more distracting on camera than it might even be in person."

• Never forget the video camera's powerful reach.

A manager for a Wall Street firm described a good stock pick during one videoconference. The camera caught a dubious colleague rolling his eyes upward. That was unprofessional, Ms. Klaus says. But at a live meeting, the coach adds, "there's a chance not everyone in the room would have seen it."

Oblivious that the camera was running ahead of their videoconference with San Francisco pay consultant Frank Glassner, top officials at a diversified French company debated the wisdom of his advice. He saw and heard every word. "Frank's here," Mr. Glassner says he chimed in, though, he adds, in this case the surprised executives "didn't lose a beat."

An attorney working from another location for a big New York law firm fell asleep during an internal videoconference last December. As his head fell forward, "he almost brained himself on the conference table," a partner recollects. "We were all laughing." Luckily, no one heard him snore, though perhaps that's only because he had punched the mute button.

• Avoid culturally insensitive gestures.

Large hand and body motions make many Asians uncomfortable. They believe "you have to have long-term relationships" before you are demonstrative, explains Chris Duncan, global leader for communication resources at Dow Chemical. About 70% of the company's 43,000 global employees have access to Dow's more than 150 videoconferencing units.

• Quell video interview jitters by practicing.

Before you meet a recruiter on a videoconference, you might rehearse at a Kinko's. Enlist a distant friend to role play the recruiter, critique your body language and sharpen your delivery.

Alternatively, make a video at home. Review the clip without any audio "to see where your little quirks are," Ms. Klaus recommends. And turn your back to the screen before you listen to your replies. If you sound like a mouse -- she dubs this "squeak speak" -- practice boldness.

Write to Joann S. Lublin at joann.lublin@wsj.com.

To see past Managing Your Career columns, please go to CareerJournal.com.