How do I structure a longer answer/essay style answer in an exam?

The most important thing to remember about answering these longer-style questions in an exam is to PLAN! It might feel like you don't have a lot of time, but just spending five minutes before you start writing planning your argument will save you a lot of valuable time later on. READ the question thoroughly and make sure you understand what it is asking about the text. Exam-questions like this are usually thematically based, so try and get together 4 or 5 main points that discuss structure and language in relation to the theme. It might be useful to draw a spider diagram, with the question in the middle, to get your thoughts to flow.  

Once you have decided on your points, use the PEE (Point, Evidence, Explain) structure in order to discuss them. For example, in a question that asks you to discuss symbolism in Steinbeck's Of Mice And Men:

P: Curley's Wife in Of Mice and Men symbolises danger

E: She wears red and she lingers around the men's sleeping quarters (remember to use a direct quote here in order to get high marks)

E: Red as a colour signifies danger, as it is the colour of blood and often equated with anger. Coupled with Curley's Wife hanging around the men's bunks, where she is forbidden, it works to suggest she is a dangerous character, as she does things outside of the rules.

If possible, try and link each point to the next. You can easily plan for this in your initial spider diagram, by numbering your points. 

You must conclude your answer, even just with a few brief sentences summarising what you have discussed in the answer. Don't say anything new. The last sentence should answer the essay question.