I’m the copyeditor for an employee newsletter at a place where I used to work full-time. I’m an excellent choice for that job (if I may say so) because, in addition to my editorial skills, I know many of the people there. That means it’s easy for me to catch a misspelled name or an incorrect job title.
Other parts of the job are not so easy. For example, the last newsletter mentioned that someone on the staff had just won third place in a powerlifting competition. I happen to be married to someone who used to be a powerlifter, so I know that it’s a specialized form of weightlifting. Google to the rescue – I was able to track down the event and confirm that it was a weightlifting (not powerlifting) competition.
Another problem is that my eyes and brain often do an “I know that already” leap over something that I should check for accuracy. When I see the name Katherine, for example, I assume it’s spelled correctly. But wait a minute! Many women (Katharine Hepburn, Katharine Graham, Katharine Ross) spell it with an a, not an e, in the middle.
Good editing requires much more than a knowledge of English usage. Sometimes you need psychology: A sentence that’s grammatically correct may still hit someone the wrong way. Knowledge of history and politics is occasionally required. For example, people who lived in the British Isles used to be called subjects; nowadays they are citizens.
If you’re a serious writer, try to cultivate friends with a wide background in a variety of subjects, and ask them to read your stuff before you send it to a publisher. Copyeditors perform a great service for writers, but you don’t always have to pay a professional to get good advice. Sometimes that extra pair of eyes belonging to a friend or family member can make all the difference.