What are the different kinds of editing?
Developmental editors help develop a project starting from very early in the writing process, either before a piece is written or during the creation of the first draft. More common for non-fiction projects, developmental editing helps an author organize her ideas and decide on a structure for their effective presentation.
Fiction writers often use writing groups and/or beta readers throughout the writing process — an economical way to get early feedback.
Substantive editors come into play once you have a completed manuscript. They look for things like consistency of style and characterization, readability, plausibility, and other aspects of craft.
Copyeditors look over your text in its (almost) final form. They look for errors in spelling, grammar, punctuation, and word usage.
Proofreaders look for typos and errors that may have been overlooked—or possibly introduced—in the copyediting process and will also catch problems with formatting. A final proofread of every version of your book is always a good idea.