The job of a copyeditor is governed by what is known as “Five Cs.” He has to work on the copy for clearness, conciseness, correctness, completeness and consistency. Copyeditor has to take care of the flow of the text, fairness, accuracy and sensibility. Copyeditor also has to take care that legal problems have been dealt with adequately. If the copyeditor finds any ambiguity and anything that is questionable, he has to discuss with the author and get the problems solved. Coy editor is the only person who reads the entire before it goes to printing.
Now how to learn copyediting? There are many organizations imparting training in Copyediting. The training duration may vary anywhere from two days to six months. I will recommend joining a two months course if it is a full time training program. Many online programs also are available. Many universities and colleges also provide training in Copyediting. With regular feedback from an experienced copyeditor from the side of your part time employer, you can develop your Copyediting skill regularly and simultaneously earn and by the time you finish your studies you will be in a position to seek employment as a full time Copyeditor or a part timer.