You're at your desk by 8 a.m., wouldn't dream of pocketing a single box of binder clips, and haven't worn flip-flops to work since your lifeguard days. But there's more to keeping your nose clean at the office than hitting deadlines and following the employee manual. Some of the most seemingly innocuous acts can kill your shot at that promotion—or worse, land you on management's hit list next time layoffs roll around. So avoid the following seven fatal workplace mistakes at all costs.

Abusing technology Think one little email rant about your boss to a sympathetic pal can't hurt you? Think again. A recent American Management Association study found that 25 percent of companies have fired employees for email misuse. And 26 percent of businesses have given workers the axe for browsing sites they shouldn't. "Misusing the technology in your office is the number one career killer," says Cynthia Shapiro, former HR executive and author of Corporate Confidential: 50 Secrets Your Company Doesn't Want You to Know—And What to Do About Them. Thanks to computer monitoring software, "you're no longer invisible." So the next time you want to shop online for a new pair of pumps, vent about management via email, or burn up the phone lines with your latest childcare crisis, do it at home.

Butting heads with the boss You don't have to invite your boss out for happy hour, but you do have to build an amicable partnership with her. "If you don't have a good relationship with your boss, your job is in jeopardy right now," Shapiro says. "Your boss can put a raise freeze on you that will last your entire duration at that company." Not only that, a bad write-up in your personnel file can haunt you any time a future employer calls to check references.  Unless you're working for an abusive Neanderthal—in which case you might want to dust off your resume—treat your boss as though you're self-employed and she's your biggest client, Shapiro advises. A supervisor who is unsure of your commitment will have trouble grooming you for the next rung. 

Settling for a support role "Support roles are dead ends," says Penelope Trunk, author of Brazen Careerist: The New Rules for Success. If you have your eye on the executive suite, Trunk advises getting out of HR, marketing, or customer service. Instead, move into a department that's responsible for the company's bottom line, such as sales, finance, or business development.In meetings, too, avoid playing the servile mother hen who takes notes and ensures everyone's had a chance to voice their opinion, says Michele Lodin, a veteran HR executive at Advanced Medical Optics, Inc., in California. Instead, focus on the job you were hired to do and fearlessly offer up your expertise.

Confiding in HR Contrary to popular belief, your human resources representative is not your friend, advocate, or confidante. "The role of human resources is to support the company, not you," says Trunk. "If you need support, hire a career coach." Complaining about your boss to HR is like griping about your husband to your mother-in-law and expecting her to keep quiet. Ditto for voicing concerns to HR about your health, family, or ambivalence toward returning to work after maternity leave. "You cannot tell them anything that would make you appear to be a threat," either legally or in terms of job performance, Shapiro says.

Playing the Negative Nelly Openly complaining about company practices is career suicide. The company may tolerate whiny old-timers for their invaluable expertise, Lodin says, but no one's going to entrust them with a leadership role. "Negative people are always at the top of the layoff lists. Always, always, always," Shapiro says. And rookies—who usually have an easier time seeing what standard operating practices need changing—should avoid criticizing right away. "You have to earn the right to complain first," Shapiro adds, "and that means showing respect for the policies and processes that are already in place."

Not dressing for success If you're a mid-lifer who hasn't updated her wardrobe or haircut in a decade, it's time for a makeover. To management, your outdated style screams "outdated thinker," Shapiro says. Likewise, a 20-something who dresses like Lindsay Lohan screams "flighty and irresponsible." If you want to move up the totem pole, you have to dress the part: You have to wear what management's wearing.

Succumbing to temptation Considering we spend much of our waking lives at work, it's natural to want to shoot the breeze with our colleagues. But Lodin warns against developing a reputation as the social butterfly who's always gossiping, taking long lunches, and conversing instead of working—none of which will go unnoticed by the powers that be, all of which could render your career DOA.

Career makers:

Ways to zoom to the topOwn up to your mistakes. Apologize for the blunder, then move on. Now's the time to put your head down and work hard.

Build alliances. Cozy up to everyone from the receptionist to the VP of sales. The more co-workers you help, the more will help you.

Specialize. Don't just develop web sites, develop web sites for women's cancer research. The more fine-tuned your skills, the more valuable you are.

Educate thyself. Stay on top of industry trends. Besides gaining a deeper understanding of your company and job, you'll impress the bigwigs.

Network incessantly. Stay in touch with industry contacts. That way, if you get laid off, you won't have to start your job hunt from square one.