By now, everyone knows the basic mistakes to avoid at work: no flip-flops, no swearing, no offensive downloads, and no irate E-mails. But there are plenty of other faux pas that can do harm to an employee's or manager's reputation in the office or with clients. Sometimes, these lesser-known errors are tough to learn to avoid. Luckily, the careers bloggers who contribute to U.S. News's On Careers: Outside Voices have come to the rescue. Here are eight mistakes they've spotted that you might not have known you were making:

Talking about politics: Political opinions uttered around the water cooler can hurt office relations—especially if you're the boss, says G.L. Hoffman, chairman of JobDig and author of What Would Dad Say. Bosses who openly favor a particular candidate will appear to be taking sides with employees who favor the same one, Hoffman says. Even for nonmanagers, politics is a quick way to damage relationships with clients or vendors.

Quietly absorbing the increased price of gas: You're paying through the nose to get to the office every morning, so why not take advantage of it? Blogger Andrew G.R. of Jobacle says this is a great time to ask for a raise. You might not get it, but you will have laid the groundwork for future negotiations, he says. Also, if you get turned down, you can take the opportunity to lobby for a telecommuting day each week.

Writing modest self-appraisals: There is plenty of reason to show humility at the office—most of the time. When it comes to writing your self-appraisal, however, modesty is ill-placed, says Suzanne Lucas of Evil HR Lady. Your boss is almost certainly too busy to keep tabs on all your accomplishments throughout the year. The self-appraisal is an ideal time to show off all the terrific projects you've helmed and clients you've brought on. Just be honest, Lucas says.

Spending too little time listening: It's easy to think that your job is to be a big thinker and a great achiever. But much of the time, the people around you just need to be heard. A good listener can stand out in an office of big shots. Michael Wade, author of Execupundit, writes that he once knew an executive "whose career success was widely attributed to his extraordinary ability to listen. When he was with you, he was with you."

Downplaying your mistakes: Sure, you're nervous in the face of your error, but acting like it's nothing won't make it nothing. Your boss might very well end up more concerned with your blasé attitude than with the mistake itself, says Alison Green of Ask A Manager.

Not using your vacation time: You think you're too busy and you think it's too expensive, but take a vacation anyway. "Vacation is given for a reason—you're not impressing people by failing to take it," writes Grant Harmon, who blogs at Newly Corporate. "In fact, you're proving that you're not able to balance work/life." Use the time to restore your energy. Then head back to the office looking refreshed and ready for work.

Talking yourself out of dreaming: Sure, dreaming can lead to wildly ridiculous ideas and outrageous goals, but outrageous goals get achieved all the time. Still, most people shut their dreams down pretty quickly. Curt Rosengren of The M.A.P. Maker suggests, instead, that you assume "the only possible outcome is success, and then challenge yourself to prove how that can happen." You're talking away the critic and forcing yourself to get creative.