Assuming you have read the story you are about to teach, an effective way to prepare to teach/discuss it is to list a few choices characters face and be prepared to ask your students what they ought to do.
Should Frodo have put on the ring in Mount Doom?
Should Sam have put it on in the Orc fort?
Should Eowyn have gone to the Battle of the Pelennor Fields?
Another effective way to prepare is to identify some potentially fruitful comparisons, especially between actions by characters. But character traits, settings, and even motifs can also be quite useful.
Don’t make comparing complicated. Just ask things like: When Frodo got to Mount Doom, what did he do? What did Sam do? What did Gollum do? How were Frodo and Gollum similar? How were they different?
Then you can even discuss responses to the actions:
Did Frodo deserve the fame he attained?
Keep it simple and watch how your students plunge into the story.