When my students were learning about Literary Analysis in College Composition, we read Anthem by Ayn Rand together as a class. Anthem is a short, easily read, but very thought provoking, dystopian novel. It is filled with great discussion fodder. You can also receive a classroom set of it free through the Ayn Rand Institute.
Then as a class we looked at it through many different lenses. We discussed how it would work with Reader Response, with Deconstructionism, with Feminisim, with Marxism, with Historical Analysis, et cetera. We discussed this in depth, using only one or two of the literary theories a day.
After they had a firm grasp on the many different 'lenses' they could look at a text through, we moved on to a classic book of their own choosing. They each wrote an essay about the book using the Literary theory of their choice. It was highly effective, and I felt I had prepared my seniors for how to write about a book on a college level.
Good luck to you with your lesson.
I would say the best method of looking at different interpretations or something you read is by asking yourself a few imortant questions:
What point of view is the story told in and is it a reliable narrator?
What background do we know about the author that can reveal important information in the story?
What literary devices or figurative langugage does the author use and how can those be interpreted?
Are the main characters like the protagonist and the antagonist well rounded characters or are they flat? ( which may lead to various interpretations)