The answer is this: It is entirely up to you.
If you've taken your book as far as you can take it—and either you're stuck, or you just need a fresh pair of eyes--then you might consider finding an editor.
Taking your book as far as you can take it means different things to different authors.
It could mean you've written a first chapter and an outline and you want feedback before you go any further. Or it can mean you've written several drafts of an entire book or proposal. Only you can say if you've taken it as far as you can go for now.
Timing is key.
If you feel you are ready to work with an editor, make sure you are at a point when you can benefit from stepping back and gaining perspective—and when you are ready to leave the book alone for at least a couple of weeks, or several weeks, while the editor does her thing.
What If You Can't Afford a Paid Professional?
You may be able to find that fresh pair of eyes you need from a trusted literary friend rather than a paid professional. Or you may have the good fortune to find a writers' critique group that supports you with constructive suggestions.
No matter where you go, use all your powers of discernment.
Before you give your precious work in progress to anyone, rely on your intuition and common sense as well. A so-called friend or colleague who secretly envies your talents and opportunities is the worst person you could ever give your book to.
What's also key to remember is that it takes skill to give useful feedback on a book. Not everyone who loves to read or even who writes well has the skills to give you the kind of detailed, specific, constructive, and honest feedback you might need to take your book to the next level.
So be selective about whom you give your book to for feedback, whether it's a paid professional or a trusted friend.
Be selective in hiring a professional editor.
- Talk to the person. Clearly state what your hopes and desires are in terms of working with an editor. Ask lots of questions.
- See if you feel in your heart if the two of you are a good match.
- Make sure that person takes a good look at a sample of your work before making a decision to take you on.
- You want someone who is selective, too. Someone who can be of service to the project and the author. Someone who cannot connect to the material cannot really be of service.
- Make sure they've got testimonials on their website and/or can give you references to contact.
- Beware of people who tell you that in order to get published you must work with a freelance editor.
- Be even warier of those who tell you that if you hire them, or if you hire the editor they refer you to, that they will get you published. No one can make such a guarantee.
What a good professional editor can do is help you develop your strengths and fix what needs fixing so that your book is in optimum shape, whether you're pursuing the traditional publishing path or planning to publish independently.
Wishing you lots of happiness and success with all your writing endeavors!