Historians, as a discipline, rely on the Chicago Manual of Style, and the best and easiest source for this style is A Manual for Writers of Term Papers, Theses, and Dissertations by Kate Turabian. It is only $14 (regular price), and the department strongly urges you to buy your own copy to consult when you are writing papers. There are abbreviated versions of this style on line, but they do not cover all possible source types.
UW — Madison Writing Center Chicago/Turabian Documentation
University of Georgia Research Guide
Bridgewater State College offers a collection of style guide examples
The Ohio State University Turabian Style Guide