What do editors do – the three levels of editing

To make your writing the best it can possibly be, it is a wise investment to have it professionally edited. Authors are too close to their work to look at it objectively or to spot any weaknesses or errors that might annoy potential readers. During the editing process your manuscript should undergo the following:
Structural editing (or substantive editing) looks at the big picture to make sure the manuscript works as a whole – plot, characterisation, story flow, scene transitions, tense, voice, presentation etc. (more applicable to fiction than non-fiction).
Copy editing examines a manuscript more closely for problems with consistency, language, clarity, grammar, spelling, punctuation.
Proofreading is a final check before sending your manuscript to a printer or publisher to make sure no new errors have been introduced during the correction process and to check that formatting is correct.

ps editing