Before getting started on the editing portion of your project, you should know the kind of editing you're looking for. The following is a brief outline of the 3 basic categories of editing:

proofreadING

Proofreading addresses the finer details of a work, including typographical, mechanical, spelling, and punctuative errors, while also attending to any formatting or layout inconsistencies.
 

copy editING

Copy editing thoroughly inspects issues of grammar, phrasing, diction, and consistency of style and mechanics. It also includes the standardization of the above-mentioned proofreading elements.
 

substantive/content EDITING

Substantive editing may involve close communication with the author to ensure elements are in accordance with the author's vision for the piece. Substantive editing will address structure, including the re-arrangement of sentences or paragraphs, to ensure a logical flow of content and will also include ample detailed feedback.