When reading a primary source, consider the following to evaluate and interpret its content:
How reliable is the author's account? Was the author an eye-witness to the events described? Was the document written immediately, or did some time intervene between the event and documentation? Was the author in a position to fully understand her subject (e.g. European travel writers describing foreign customs)?
What was the author's purpose? Was the document intended to persuade or convince the reader? Was the intent to deliver an impartial recounting of events? Was the document intended only for internal record keeping, as in a business or administrative office?
Who was the author's intended audience? Was the document written for posterity, to present a specific view of the past (e.g. autobiography)? Was the document written for public consumption at the time it was written (e.g. newspapers)? Was the document private, and never intended for the public (e.g. personal correspondence, diaries)? How might the intended audiences influence the author's account?
What is the context of the document? Does the language used have the same meaning now that it did in the past? How or why was the document created? How does the document relate to other contemporary records, and to what we know about the time period and persons involved?
Can your corroborate the source with other evidence? Do other primary sources support your interpretation of the document in question? Can you justify why the document in question may not conform to similar contemporary sources?