How do I answer a question which requires source analysis?

The most common question in history A-level source papers is “With reference to these sources and your understanding of the historical context, assess the value of these sources to an historian”. The most important thing to notice here is the wording “with reference to THESE sources AND your understanding of the historical context”. Students who get top marks will always have the source material lead their response to the question. For example, if you were answering a question on American attitudes to the African American civil rights movement you would have to first study the sources to find textual details that would provide evidence for your argument. If the source detailed abusive or negative treatment of protestors this detail could then be supplemented with your own knowledge of the historical period.
Students who wish to get the top marks should always pay attention to and remark upon the following: the PURPOSE of the source (this can be found in either/both the nature of the source, e.g. a public speech given by a politician, or the details of the source, e.g. if the author states their intention in creating the source), the intended audience (paying attention to how the type of audience might change the contents of the source, e.g. a source created for an illiterate audience will be very different to one created for socio-politico elites), and the time period (understanding the values and concerns from the society in which the source has been drawn).  With all of these elements it is not enough to repeat what the source says but to take your analysis one step further, asking how the context, audience, and purpose both shape the content of the source and affect its reliability to historians. These elements will all help in determining whether a source provides reliable evidence or is a claim/opinion.