Know which citation style your paper requires. Your assignment should specify the style required. In general, literature and humanities papers require Modern Language Association (MLA) style, while papers in education and social sciences use American Psychological Association (APA) style. Most science papers use American Medical Association (AMA) style. Two other styles, Turabian and Chicago, are general reference styles used in all subjects. If an assigned paper pertains to the law, your professor may require the Bluebook style used by lawyers.
Keep a running list of all your references. This will save you time later because you won't have to look up the sources a second time. By keeping a list of all references, you will have what you need to compile a bibliography/reference page at the end of your paper.
Use proper footnotes or endnotes, if required by your professor. If you paraphrase or quote material from a reference, it is important that you cite it in your paper. In general, you should provide the full citation in an endnote or footnote the first time the reference appears. In subsequent references to the same work, you can use an abbreviated form of the citation -- usually only the author's name and/or the page number.
Complete your bibliography page. Be sure it is properly formatted and includes all of your references. Fortunately, word processing software makes formatting a paper much easier than it used to be.
Format your paper and proofread carefully, making sure you have cited all materials used and in the citation style required for your paper.