Study on your own. Two often-used style manuals Chicago Manual of Style , 14th ed. It's hard to really learn Chicago style without using it to edit something, though. Read James Kilpatrick's column on language in the Scene section of the Sunday Seattle Times , and William Safire's column in the Sunday New York Times Magazine . Contains updates on grammar, spelling, punctuation, style and usage, and computer technology, as well as helpful articles on topics ranging from choosing the right dictionary to avoiding libelous words.
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Leave the subject line blank. Out of print but good. Available at the Seattle Public Library. Consider subscribing to freelance-l, a listserv for publishing industry freelancers. Anyone starting out in the business is welcome.