You can start by reading the eNotes discussion of Lee's style (see the link below). There you will find information about the point of view, setting, symbolism, and humor in the novel.
If you are writing an essay, you might want to make note of each of these aspects of her technique and give examples from the book in support of each one. For instance, many people have pondered the symbolism of the mockingbird and how it relates to the title. Many states prohibit the killing of any songbird, and some people consider the killing of a mockingbird to be bad luck. Are there any characters that might make you think of a mockingbird, of an unfair killing?
You might point out that she uses humor in telling her story. Is it there just to entertain, or is does she use it as a subtle way to criticize society?
From what point of view is the story written? Is there any importance in that?
Take a look at some of the critical essays in the study guide as well to get some ideas.