Developmental editing (may also be called structural or content) – looks at the book’s big picture and overall structure in nonfiction or plot and characters in fiction. Developmental editors may assess a book idea, outline, or early draft to tell authors what works and what could be better. The big picture questions need to be answered first before an editor ensures your words are polished and used correctly.
It’s always sensible to follow due diligence in submitting your first draft of your book to an editor by making as fool-proof a copy as possible for you because first, it is your own creation, and secondly, a horrid draft sent your editor can end up frustrating both you and him or her. Make your own corrections to the extent you can, so that will make the job of your editor that much lighter and the end result would be a lot more effective.