Carefully read the assignment. Check and double check to be certain that you understand what you are expected to write about. Most teachers and professors are more than happy to answer any questions you might have.
Brainstorm. Make a list of all the possible topics you can think of. At this point, no idea is a bad idea. You may want to ask a few friends or fellow students for suggestions.
Narrow down your list of ideas. Consider the topics and types of stories you enjoy, and eliminate any that you find uninteresting.
Choose three or four of your favorite potential topics. Make a short, tentative outline for each one. Consider what subpoints you would like to address for each one. Think about the characters in each story. What about their personalities interest you? Are there any with whom you identify? What character traits do they exemplify? Or, what flaws do they show? What things do they have in common? These questions will help you decide which direction to go with your paper.
Check the internet and library to make sure there is an abundance of sources. Eliminate any topics that do not have enough information to support a paper. Make sure you have plenty of credible sources you can refer to.
Pick the best topic. If you are still having a hard time deciding, your teacher may be able to offer some input. Check your topic against the original assignment. Does it provide a good opportunity for you to meet all the requirements of the assignment?
Make the topic more general or more specific as needed. As you do research, you may find that your topic is too specific or too broad. Feel free to adjust it as needed.