In the study of history, perspective is everything.
A letter written by a twenty-five-year old medical student will differ greatly from a letter written by a scholar of health science practices. Although the sentiment might be the same, the perspective and influences of these two authors will be worlds apart.
A historian doesn't look for the truth, since this presumes there is only one true story. The historian tries to understand a number of competing viewpoints to form their own interpretation – what constitutes the best explanation of what happened and why.
Who authored the source?
Who is the historical actor?
Who isn't represented in the historical record?
What is the document about (what points is the author making)?
What kind of audience did the author intend to reach?
What aren't you finding? What are the silences in the record?
When did this take place?
When was the resource created or written?
Where did the happening occur?
Where was the resource created, published, and/or disseminated?
Why did something happen the way it did?
Why was this resource created? (also involves the intended audience)
Examine your biases
What do you bring to the evidence that you examine?
Are you inductively following a path of evidence, developing your interpretation based on the sources?
Do you have an ax to grind?
Did you begin your research deductively, with your mind made up before even seeing the evidence?
Use as wide a range of primary source documents and secondary sources as possible
Adds depth and richness to your historical analysis
The more exposure you have to different sources and viewpoints, the more you have a balanced and complete view about a topic in history
More exposure/viewpoints may spark more questions and ultimately lead you to unravel more clues about your topic