The Chicago Manual is a comprehensive style manual used throughout the U.S. publishing world and contains much useful advice on matters of punctuation, capitalization, and word choice as well as on the documentation of sources.
A well-respected guide from Purdue's Online Writing Lab
Citation Managers
Zotero: The Tri-College Libraries recommend Zotero, a free online app that can format your bibliography, keep your citations organized, and even save your articles in the cloud so you can access them later from the library, home, or a cafe.