Determine when you need to cite your sources. Nova Southeastern University lists three occasions when you must cite sources: when another person's research, ideas or theories influence your work; when you introduce key information that supports your work, disputes your theories or offers definition or background; and when you use facts or figures that are not common knowledge. Most class assignments require at least two supporting sources for every key point you make in your paper, while literature papers frequently require many more, Nova says.
Cite your source in a way that does not interrupt the flow of your text. You can do this, Nova says, with a construction such as "Smith (1968) discovered...." Or, you can state the fact and follow it up with: (Smith, 1968). Or, you can introduce a quote: "Smith says, 'discoveries are ...' (p. 14)."
Direct quotes should always have a page number associated with them. You can even group citations when more than one person agrees, as in "these discoveries were made independently (Smith, 1968; Johnson, 1968)." Purdue Online Writing Lab says that if there are two authors, refer to them as Smith and Johnson in the text, or as (Smith & Johnson, 1968) in parentheses. If there are more than two authors, use the abbreviation "et al." after the first author's name.
Use information from your notes or lectures if it is appropriate to your argument. If you want to cite information such as something your instructor said in class last week, use it with an in-text citation. Purdue recommends either adding the parenthetical citation at the end of the statement, as in (Jane Smith, personal communication, August 20, 2010) or incorporating it into your statement, as in "Jane Smith told the class A=B" (personal communication, August 20, 2010). This can make a good impression--if you use only strong and relevant information and cite it properly in APA format.