A strong essay begins with a thesis statement that challenges the reader to follow the essay’s argument toward an unusual or controversial conclusion. So, if you began with “The Iliad is a story about the Trojan War,” you would not have a good thesis statement. But if you started with “The Iliad is outdated and no longer readable in modern times,” you would have stated a controversial (but, in my opinion, untenable) opinion. Look at the epic and find the most unusual thing about it that piqued your interest as you read it, and go from there. Were the characters psychologically convincing and consistent? Was Helen worth all those deaths? Who were the villains, if any? What part of the story did Homer not discuss, but which you wished he had? etc. So, the answer is: Find what interested you about the epic, and defend a controversial point of view.