"Your e-mail, sent internally or externally, is probably more important in affecting your career than anything else you write," says Dianna Booher, CEO of Booher Consultants, a communications training firm that has taught execs at 22 of the largest 50 corporations in America how to write and speak better. When you send e-mail, Booher adds, "you're documenting what you do."

Think about it: What kind of document do you send to your boss most often? What document do you receive from your staffers most often? E-mail. Treat e-mail without enough thought, and you will limit yourself professionally, Booher says.

In her new book, The Voice of Authority: 10 Communication Strategies Every Leader Needs to Know (McGraw-Hill), Booher outlines 10 things you should never put in an e-mail. Of these 10 e-mail mistakes, which one do executives make most commonly?

"Sloppy writing," Booher says. "They are in a hurry and they assume it won’t be passed on. They assume everyone has the context for the message. Provide a context for your comments and make sure people know what kind of action you expect."

Don’t just deliver news, she says. Make your request. Communicate clearly. And avoid shorthand, which can mask what you really intend to say.

At one client, a major real estate business, "the CEO of the company got an e-mail saying 'we need to set up more procedures on how we close on commercial property.' He wrote back and said ‘I don't understand why we need all these procedures.’" The staff wrote a lengthy explanation. He didn’t need the explanation, he just meant no, he didn’t want more procedures," Booher says. "But he worded it in a sloppy way." This wasted his team's time.