Click here for a summary of a program we produced on courses in June, 1999. Many companies that hire copyeditors give a test, so you should prepare yourself to do well.
Internships can be very useful for learning about the whole publishing process on the job.
The best way to find out is to ask companies you might like to work for. Often, a certificate in copyediting is aimed at preparing people for book and magazine work, but you can also take technical editing courses. Other kinds of companies are only beginning to discover and appreciate what an editor can do for them. There's a greater demand than there used to be. The difference between a copyeditor and a developmental editor can get pretty blurred in some situations.