Last year, two sales assistants at Steven Berger's advertising agency were up for promotion. Both women had the technical knowledge to sell the firm's services to clients, but their communication styles were vastly different. One candidate exuded confidence when she delivered presentations, speaking authoritatively and making eye contact as she moved about the room. The second candidate mumbled and avoided eye contact when she was in front of a group.

Guess who got the promotion? The first candidate, naturally. "It really was a no-contest decision," says Berger, president and CEO of PIC-TV in Los Angeles.

Connie Glaser, an Atlanta-based management consultant, isn't surprised. "No matter how good you look on paper, your communication skills will determine whether you get promoted," says Glaser, author of Swim With the Dolphins. "If you impress your boss with your verbal and written communication skills, the boss will assume that everything else you do is positive. It's called the halo effect."

Indeed, what you say and how you say it can make or break your image at the office. In a recent survey by OfficeTeam, nearly half of the more than 500 respondents said that an individual's communication style has the greatest impact on his or her professional reputation--one that can mean the difference between a career that soars or sinks.

"You could be the best chicken plucker on the planet, but if you're irritating, if you have nothing nice to say about anything or anyone, if you interrupt people, if you give one-word answers, if you make others feel uncomfortable, you'll always pluck chickens--and you'll never manage the pluckers," says Susan RoAne, the San Francisco-based author of What Do I Say Next.

Why are skilled communicators so valued? Because they can build rapport with coworkers and business associates, which can help move projects along more efficiently, according to Liz Hughes, executive director of OfficeTeam.

Communication also counts in job interviews. Howard Martin*, a 39-year-old sales director for a transportation company, interviewed 30 candidates for three national account manager positions in the past year. Though the individuals Martin hired had varied experience, each effectively articulated his qualifications. "They answered my questions clearly and concisely," Martin says. "I wouldn't even consider hiring the guy who whispered or the one who shouted. I wouldn't trust them not to speak the same way to customers."

Communication faux pas fall into two categories: content and tone. "The way we deliver our words signals the emotions behind the content," says Renee Grant-Williams, a Nashville-based voice coach. "It's not always what you say, but how you say it."

Here are 13 communication blunders that could tarnish your reputation.

Interrupting. "It shows that you're not listening, and if you're not listening, you can make mistakes or misjudge a situation," Glaser says. "It also can make you come across as ego-centric, rude and disrespectful."

Whining. "You shouldn't whine and complain about something without suggesting how to fix it," Berger advises.

Speaking too quickly. "People need time to digest what you're saying," explains Grant-Williams, author of Voice Power. "Otherwise, they'll lose what you've just said or miss part of what you're saying next." Instead of running words together--which also can create the impression that you lack confidence--try to speak in sentences.

Relying too much on humor. "If everything you say is iced with sarcasm, you're asking people to do the work of reading between the lines," RoAne explains. "Essentially, you're saying, 'What I'm saying isn't true, so figure out what I mean.'"

Badmouthing coworkers. "This is a holdover from school days, when tattling was a gross offense," says Marlene Smith*, a city editor at a major newspaper. "If you demean a colleague to a boss, you're being undignified and hurtful."

Being too direct. The "let-me-tell-it-like-it-is" trait is typically male--and it's usually hurtful. Combative communication doesn't help build teams or alliances--the cornerstone for success at work. "Many people who perceive of themselves as honest use their honesty as a guise for brutality," RoAne explains. "I have never met a person who said 'I tell it like it is' who didn't end up being a jerk." The solution: Try to use 'I' messages instead of 'You' messages.

Becoming overly emotional. "Once you cry at work, you lose all credibility," Glaser cautions. "Women have difficulty climbing the corporate ladder because they often become emotional when receiving feedback so managers are less likely to give them the candid feedback they need to perform at a higher level." Lawyer Malcolm Carpenter* has done just that: "I'm reluctant to offer constructive criticism to the younger lawyers who get extremely defensive. I don't want to argue; I want them to learn and move on."

Sending mistake-laden e-mail. "Remember that spell-check doesn't," RoAne says. "If a word actually is a word, but the wrong word, it will make it through spellcheck." Mistakes in e-mail--whether in grammar, syntax or spelling--convey that you lack a grasp of the language and that you're sloppy. And if you're a manager who errs in writing, rest assured that subordinates will take notice. "Sometimes, my supervisor's e-mails are so cryptic and poorly written that I'm not even sure what he wants me to do, because so many key words are omitted or garbled," says Tiffany Jackson,* a sales executive in the computer industry. "I'll ask a coworker to interpret, and we'll end badmouthing our boss."

Rambling. If your boss asks you for the time, don't explain how to make a clock."This is a big problem for women, who often become so engrossed in details that they don't get to the bottom line fast enough," Glaser says. "Men have little tolerance for rambling--it's one of their chief complaints about female colleagues and subordinates--so try to be succinct in every mode of communication."

Engaging in verbal one-upsmanship. It's the "mine is better than yours" syndrome, and while both genders engage in it, the syndrome is more prevalent among men. "People don't like those who speak to compete," RoAne says. "It's very off-putting."

Speaking without thinking. "When you leap in after someone has said something, you create the impression that you haven't been paying attention," Grant-Williams says. "Waiting a few seconds gives you time to think about your answer and respond more appropriately."

Failing to be courteous. "The words 'please' and 'thank you' are the three most powerful words in the English language," Glaser says. "Playing nice is important no matter what your level, but the higher you go in a corporation, the more important it becomes."

Arguing over e-mail. It's unwise to try to solve problems electronically, because meanings can get misconstrued. "This approach only adds fuel to the fire," Berger says. "If you've got a dispute, pick up the phone, or, better yet, get out of your chair, walk over to the other person's work space and have a conversation."

How can you find out whether you're committing a major communication sin? First, pay closer attention to your own behavior and how others react to you. Second, ask your boss to assess your communication style and to suggest how you might enhance it. Finally, ask a trusted co-worker to give you the straight scoop on how you come across.

The good news is that you can upgrade your communication skill. A year after getting passed over for promotion, the sales assistant at Berger's advertising agency is now poised for advancement. "She asked what it would take to get to the next level and then followed my advice," Berger says. "She took classes on public speaking, watched me put presentations together, and accompanied us on sales calls. She watched and learned. With effort, it is possible to improve."

*Names changed in the interest of privacy.

Cynthia Hanson is a freelance writer in Philadelphia. She is trying to shake her nervous habit of talking too quickly.