I'm not sure exactly where your teacher wants the thesis statement placed; however, a lot of teachers prefer the thesis to be the very last sentence in the first paragraph. If that is the case, then before that thesis sentence, it is good to introduce the book, give a little bit of what it is about, and then have a good lead-in to your thesis. So, I might start off generally by stating, "To Kill a Mockingbird" is a classic novel whose messages of justice, decency and equality will live through the ages. The book is unique in that it is narrated by a young girl, named Scout, who is a bit of a tomboy. Scout's heroes are her older brother and her father, so she tends to emulate more masculine behaviors. However,----and insert your thesis.
That is just a general idea; for sure, you need to take it and put it into your own words, but I hope that you get the gist. In writing opening paragraphs of essays, you don't want to get too specific; save examples and details for the body paragraphs. You just need to let the audience know which book you are writing on, and give an adequate introduction to your thesis. I provided some great links below that have information on writing essays and introductions-those shoule help also. Good luck-it sounds like an interesting topic!