Common knowledge. If most readers already know a fact, you probably do not need to cite a source for it. You do not need to credit a source for the statement that Barack Obama was reelected in 2012, for example.
Factsavailable in a wide variety of sources. If a number of encyclopedias, almanacs, textbooks, or reliable Web sources include a certain piece of information, you usually need not cite a specific source for it.
Your own findings from field research. If you conduct observations or surveys, simply announce your findings as your own. Acknowledge people you interview as individuals rather than as part of a survey.