How should you approach a history source-based question?

Often with source-based questions you're required to argue one source is more "valuable" or "reliable" in helping you to understand a certain subject. Therefore it should come as no surprise that you should focus closely on the information that contextualises the source; who they are (their position, political affiliation, rank), when or where they said it (who was the audience, does this influence what they are saying), the date they said it (is it a contemporary source or retrospective). Considering these details, what points does the source make relating to the question being asked- does this present reality, an exaggeration, or a fallacy? Working through methodically will, ultimately, allow you to write an informed conclusion about which source is indeed more valuable, and summerise why it is more valuable.