I recommend beginning with an example or an analogy that is related to the stereotype that you're studying. What are some common stereotypes that still exist today? Can you think of one that is closely related to the stereotypes that you're analyzing in your paper? Stereotypes exist in many capacities throughout our society, so start brainstorming!
Once you've settled on an example of stereotypes in our society that behave similarly to stereotypes from To Kill a Mockingbird, then write a sentence that connects your attention getter to your thesis. Follow this statement with another sentence that gives a short synopsis of the novel and mentions both the author and the title of the novel. Finally, insert your thesis statement.
There are a few websites that I would recommend that deal with stereotypes in the media. The primary source you should consult is the Media Awareness Center. This organization does a fine job organizing different categories of stereotypes to read and look through.