You should always be sure to cite your sources in order to:
A general rule of thumb for citation is that you should always cite:
You do not have to cite information that is generally considered to be common knowledge (i.e. Washington D.C. is the capital of the United States; or The Declaration of Independence was issued on July 4, 1776).
For most citation styles, you should at the very least include:
Beyond this, the accuracy of your citations depends on the individual rules of the citation style you are using. You will likely determine the citation style you need to use according to either: