One of the hardest but most important things to get to grips with when writing an essay is to be able to talk about language and form. It is important to talk about some aspect of this at least once in order to cover all of the assessment objectives.
If there is nothing obvious, or the form seems so much like anything else that there's nothing to say, just break it down by answering a few questions: is the narration in first person? Or is it an omniscient narrator? If it's in first person, does it feel more realistic and personal? At this point, you can look at the type of language. Is it formal or informal? Is the narrator using colloquialisms (slang phrases that are specific to a character) or is the grammar purposefully bad? If any of these are - or AREN'T - present, there will be a passage of writing that backs up what you're saying.
There are two very important things you must do once you have identified a feature like this in a text: firstly, quote an example which concisely backs up your point. If you don't, you will get marked down, and you have to also appreciate that the marker is unlikely to have a book to hand so is relying solely on the information you give them.
Secondly, play the 'so what?' game. For example, if you were writing about John Steinbeck's 'Of Mice and Men', you might make the point that the physical descriptions of Lenny and George are extremely different. Having provided evidence, you shouldn't leave that point standing but go: so what? So what if their description is different? How does that affect the book? You might then answer your question by saying 'Lenny and George's opposites highlight their mutual need for one another, with all of their flaws and benefits adding together to make them useful workers when together.' So what? Go even further: 'this emphasises exactly how close the two are, which makes the ending of the novel even more tragic.' So what? 'By providing such an emotive conclusion, Steinbeck conveys the sad futility of the American Dream to the reader with effective resonance.' That may seem like a tricky and overdone method, but it really works. Once you get used to doing it through practice, it will become natural. The best way of structuring the answer is through P.E.E. Your teachers will probably have mentioned that to you before, but Point-Evidence-Explanation makes sure you hit all of the objectives and provide a clear argument.
By using this method, you can go deep into the micro-features of a book like language and form, and link it in to the larger themes in the book.