Choosing a topic can be one of the hardest parts of writing a paper. There are so many possible things to write about, and even if you have a general idea, it can be hard to know whether your topic is a good one.
Writing a literature paper is different from writing many other kinds of papers. In literary analysis, it's not the ideas of other people that matter as much as your own interpretation of the texts you're reading. The bulk of your paper will be made up of your analysis of the text: the use of language, imagery, rhythm and repetition, word choice, the structure of the plot, or the representations of characters, emotions, events, or places. Your job is to analyze these elements of the text and through your analysis to assert an idea, or a claim, about the text, the author, or the context in which the text was written.
So what makes a good topic? A good topic is a theme that you think is represented in the text you're reading. But how do you get from a good topic to a good research question?
Once you recognize a theme in a text or texts, your next step is to determine what you think the texts are saying about that theme. Read the text again, paying particular attention to your theme. What does your interpretation lead you think about the theme or idea? This is your claim, and your paper is structured around using analysis of the text or texts to support your claim.
For example, you may be interested in looking at community or society in Thoreau's "Walden." You may have read the text and noticed a contradiction between Thoreau's claims of self-reliance and his interaction with society. You would then re-read the text, asking yourself as you read "What is the representation of society and Thoreau's relationship to it in 'Walden'?" After reading the text closely and paying special attention to these aspects of "Walden," you may be ready to make the claim that while Thoreau believed he was self-reliant, in truth he was still part of a network of people, and still part of his society and community. Or you may discover that your initial thought was wrong, and that Thoreau really did separate himself from his community in the way he wrote about.
In order to make your argument even stronger, you may want to find out more about Thoreau's role in his community by reading primary source material (letters that he wrote to friends and colleagues, newspaper articles about him or about his community) or by reading more about the context of his life in Massachusetts (the political and artistic movements of which he was part, the actual location of his cabin in relation to the town of Concord). These additional sources are used to support your interpretation, not necessarily to be the bulk of your evidence. Your evidence should primarily lie in your interpretation of the text itself.