Unless you are extraordinarily blessed, you probably are stronger as a writer in some areas than in others. A professional editor should not only point out your strengths and challenges, but also should help you triumph over your challenges by showing you how to expand your own strengths and talents into areas of the book that need them.
A professional shouldn't merely say: "The pacing is slow," or "The description is cumbersome"; a professional should show you examples of what they mean and why. A professional should offer you specific suggestions for improvement.
A professional should also be your champion, believing in you and your work and encouraging you every step of the way. Don't settle for anything less.
Taking Dialogue to the Next Level:
Let's say you're writing a novel or a piece of creative nonfiction. You might be strong on plotting but need improvement with dialogue. A professional should be able to point out examples of where your dialogue could be taken up a notch and give you pointers on sharpening, creating conflict, eliminating exposition, and creating markers that distinguish one character's manner of speaking from another's. A professional should be able to suggest ways to make dialogue move your excellent story forward instead of stopping it in its tracks.
Writing in Scene Instead of Summary:
Perhpas you excel in writing strong immediate scenes, but you're missing a character arc. A professional might suggest substituting a character's narrative summary of action with an immediate scene that expresses a turning point in the character's development or otherwise gives the reader insight into the changes the character is going through.
Picking Up the Pace:
Perhaps you excel in creating sensory description, but your pacing is slow. A professional should be able to point out areas that need streamlining or cutting to pick up the pace. Or they may suggest your substituting bits of the sensory description you excel in for long, plodding passages. Or they may suggest substituting gripping, tangible immediate scenes for bland narrative summaries.
Choosing and Working With a POV:
Let's say you've got a strong story and characters, but you're having a difficult time adhering to the point of view you've chosen for your book. A professional should understand the differences between first-person POV, various types of third-person POV, and the omniscient POV, and can show you where your POV deviates and how to fix it.
Nonfiction That Sparkles:
Perhaps you're an expert in your field and have a great idea for a book, maybe even a few good chapters. But you haven't a clear idea for how to structure an entire book. Or your chapters are adequate but not sharp enough for submission. Or you're crystal clear on your concepts in your own head but it's not coming across on the page. Or you're not sure how to go about creating a persuasive proposal. Or the competitive books section of your proposal is twenty pages long and intelligible only to you.
The right editor can help you with any or all of those issues.
If You're Looking for an Editor, Ask Lots of Questions.
This is not a regimented profession. Which is why you should ask prospective editors questions about what they can do for you. And communicate what you want, what your ideal scenario is for working with an editor.
Keepin in mind that your editor may specialize in certain areas. For example, some editors edit mostly nonfiction, while others specialize in fiction. Some editors may specialize in genre fiction, such as romance or science fiction. Some editors, like me, do both fiction and nonfiction.
Stay tuned for my post on manuscript analysis/critiques.
In the meantime, I'm wishing you lots of inspiration and joy in the process and tons of success!