Here are some tips from the L.A. Times. Write clearly and read clearly. If you do either in a rush, you are more likely to have a misunderstanding. Think about the reasons you are sending or receiving and keep them in mind as you deal with the correspondence. Factor in cultural differences and personal styles.
Some people write long and some write short.
Make sure to keep things professional and get to the point quickly regardless of your audience. If you are, you probably don't know it. But, if you hear complaints that you don't listen to feedback well or that your directives leave no room for discussion, then you may appear mean. If you intend to be authoritative, remember that negative approaches often engender negative responses. Again, know who you are corresponding with.