How should I approach source-based questions?

How you should approach source-based questions depends entirely on what you're being asked to do with the sources. Look at the question and establish what you need to do answer it. There are usually three things you will be asked to do with sources: compare a selection of them, use them to support your own knowledge, or assess their usefulness/accuracy. If you are asked what the main difference between two sources is, you can approach it almost like a piece of unseen literature. Look at the author and date of publication. Look at the content of the sources - do they agree with each other, or do they offer completely different historical viewpoints? With this type of question, you shouldn't bring in your own knowledge; the focus is entirely on what information you can pull from the sources and your analytical skills. This is true even if you are asked to comment on photographs or posters.