Each time you review a document looking for genealogical data, ask yourself the following questions about the document:
Who would have created the document, and why?
Would the document writer (e.g. a family member, a clerical person, an undertaker, a member of the clergy, a doctor, a judge, etc.) have sufficient first-hand knowledge of the recorded event?
Did the information of the event happen recently or in the more distant past (e.g. recent birth vs. a birth place recorded on a death certificate)?
How much concern did the document writer have in assuring the accuracy of the information (e.g. a court clerk for a will, a doctor recording a birth, a census taker recording who lives in a house)?
In compiled family genealogy books and local history books are the conclusions supported by evidence? Did the author cite sources. If so, then are they primary or secondary sources?