Wait until you have polished your work to the best of your ability before you turn it over to an editor.
Find the type of editor you'll need. Your editor will vary depending on what has to be done on your manuscript or article.. If you are looking for an evaluation of marketability or complex content analysis you'll need a substantive editor. For someone to do an overhaul of the content and structure of the book, you need a book doctor, and if you're looking for an editor to clean up the style, format and mechanical details of grammar and punctuation, pick an experienced and highly recommended copy editor.
See what you can see online about potential editors for your work. There are many sites online that list editors from across the country. Oner very helpful site is www.the-efa.org, the Editorial Freelancers Association's site.. You can also consult consulting-editor.com, editorialdepartment.net, copyeditor.com, and others.
You can also find editors in writing databases/encyclopedias like Writers Market.
Choose the right editor. When considering editors pay attention to the credentials and any experience they have had working on books similar to yours. For example, book and journal/magazine editing is a specialty. The publishing industry has specialized style and format preferences. A college English teacher or technical writer may not have the right qualifications to edit such a text.