How do I talk about the presentation of a character in a novel?

Here are three possible starting points:

You might first consider what the character (let's call her 'Jane') actually says in the novel, whether there are any instances of reported speech (i.e. speech in quotation marks) from them. Jane might have a habit of saying the same thing again and again for example, perhaps because the writer wants to present her as a comic character or as someone who is not very intelligent, or maybe as someone whose advice is continually not being heeded throughout the novel. These last two examples look really good together because it shows how you've taken one piece from evidence from the novel (Jane says the same thing repeatedly) and interpreted it in two different ways. Novels are very complex things and it is always useful to be constantly thinking 'This is how things appear in the novel. But what if things are more than they first seem?'

Jane might be in the novel only for a chapter or two. This doesn't mean that you have less to write about; Jane might be a poor character and the fact that she isn't in the novel very much might make a point about how the world of this novel marginalises poor characters.Alternatively Jane might be a central character, appearing in many chapters, and in this case it's useful to talk about how she has changed over the course of the story. Have her clothes changed? Does she speak with a more refined accent? Is she more caring than she was at the beginning because her brother died half way through and she's now learned the value of looking after the people she loves? Again, novels are complex. Stories are driven by change over time and characters are rarely just one thing.

It's also a good idea to use the question to show that you know what some literary devices are and how they work. There are two forms of characterisation, direct and indirect. The writer might just tell his reader directly what Jane is like ('Jane was a dreadul woman') or he might suggest she is dreadful using interesting literary devices such as metaphors or similies ('Jane grinned like a cobra...'). 

The question 'How is Jane presented in the novel?' is actually three questions which you can answer in this order: 1) What is Jane like? (this is the point you are making) 2) What ways does the writer have of telling us this? (this is the evidence for the point you've just made) 3) In light of what Jane is like, why is she important to the story? (this is the further explanation that shows you understand how characters and story work together - remember the question mentions both character and novel)