One of the major problems you have in writing an interpretive essay about literature is using references. Because your essay is expected to be primarily your own ideas, it is difficult, at first, to see how you might cite other people's interpretation in a fashion that seems natural and not just pasted at random into your work.
The way you are expected to do this in a literature paper is a function of what it means to be original. You can't really tell if you ideas are original until you read what other people have written. Before you start writing, narrow down your interpretive focus to one aspect of a particular literary work. Next, look in the MLA International Bibliography or JStor (both in the electronic resources section of most university catalogues) to find out what has been published before about your topic.
As you create your own interpretation , discuss in what ways it differs from the other interpretations you have read, and cite those in the format (MLA or Chicago) recommended by your professor.