Learn about the main elements of citation: the internal citation and the bibliography. An internal citation is a brief note that alerts your reader every time you use or refer to other people's work in your own writing. A bibliography is a detailed list of your sources, and usually comes at the end of the paper. Both are important because they give credit to your sources and because your reader needs to know where you got your information. Properly citing sources will also protect you from charges of plagiarism --- passing someone else's words or ideas off as your own.
Learn how to insert internal citations. Internal citations can be parenthetical --- a reference to the source appearing in parentheses in the body of your paper --- or footnotes. They should appear after every quotation, summary, paraphrase or use of data from your source materials. How the citations will look will depend on the citation style you use.
Choose a citation style. The citation style will tell you how to format your internal citations and bibliography. There are several, each designed to serve the needs of a particular profession or academic discipline. According to the handbook Research and Documentation Online, the most commonly used citation styles are MLA, APA, Chicago and CSE. Check to see whether your instructor or publication has a preference.
Find a good style guide and follow it to the letter. Each citation style has its own detailed rules of punctuation, capitalization and formatting for each type of source. You can find style guides online or as hard-copy handbooks.
Write your paper, adding internal citations as you go, so you don't forget from where your ideas and quotations are coming.
Build a bibliographical entry for each source cited in your paper. This way, you won't miss any. Never put a source in your bibliography that you haven't cited in your paper. Make sure to distinguish between different types of sources --- the entry you create for a book chapter will not be the same as the entry you create for an interview, an article found in an online database or a Web page.