How do I approach a question that asks me to analyse sources?

The first thing to keep in mind for source questions is to cover all the sources in your answer equally. In an A Level question, you will usually be given 4 and it's perfectly fine to structure your answer as a source by source analysis to make sure you get equal coverage, bracketed by a short introduction and conclusion. The next thing is to read through each source carefully and keep three areas in mind for each source - content, context and the exact wording of the question. For every source, you should discuss the actual content (of say, the letter or the speech) and apply your own knowledge to evaluate this content - from what you know, is it true? Does their language imply something interesting? Then, apply historical context - who is writing/speaking? Why have they produced the source? Are they someone significant from the period? Linking this back to the content will make the analysis more sophisticated as you demonstrate an awareness of how the context informs the content of the source. Then comes the most important bit - it must all link back to the question! This can differ - but, for example, if the question is asking which source is most useful, use your evaluation of the content and context of the source to make a conclusion related to the source's usefulness! Perhaps the content is inaccurate, or the author has an agenda you know of, and this limits usefulness. In any case, ending each source analysis with a sentence that links back to the exact wording of the question will help keep you on track.