A primary source can tell you a lot about a specific event, person, or period but they must still be checked for relevance and legitimacy.
Consider what your sources reveal and what they don't.
Purpose and motives of the author
Why do you think the author wrote this?
Who is the author and what might be his/her place in society?
What evidence in the source tells you this?
Argument and strategy used to achieve these goals
What kind of case is the author trying to make?
Is the author credible? Why?
Who was the intended audience at the time this was created? Was it meant to be public or private? If so, whom was it meant for? For example, a letter to from a soldier to a mother or wife might mask the atrocities of war. How might the content differ if he wrote to a father or brother instead?
Presuppositions and values (both in the text, and our own)
What presumptions and preconceptions do you (as a reader) bring to this text? For example, are there parts that you find objectionable, racist, sexist, but readers of that time period might have found acceptable?
How might the difference between our modern values and those of the author influence the way you understand the text?
What does this text tell you without outright telling you?
How might this text support an argument you've found in a secondary source?
Relate your source to other texts
What patterns/ideas regularly appear throughout your sources?
What major differences appear in them?
Can these be supported by other primary or secondary sources?