I agree with mwestwood. Whatever your thesis is it needs to be something that can be argued. We can't really argue that mindless following of ritual can be harmful--that's a common sense issue. What could be argued is something like "The mindless following of ritual in Shirley Jackson's "The Lottery" is shocking, yes, but no more so than the mindless rituals observed by modern society," or "The use of a scapegoat in Shirley Jackson's "The Lottery" is appalling, but this is still a trend followed in our more modern society."
"The Lottery" is wonderfully vague in terms of time and place; it could be set in virtually any recognizable time in any recognizable place. To that extent, then, this is a story which has plenty of room for commentary. I might make the case that though the practice of a lottery seems barbaric and arcane, this story is still relevant because such things do still happen all over the world.
I think that this is a great topic on an even greater piece of literature. There are many tracts one can take with such a topic. I think that a great point of commentary might be on how the story depicts the relationship between the individual and the community. Reading about Tessie’s predicament makes one fully understand where the individual stands in their dynamic with a social order. The fact that the community negates her own voice and conducts its “tradition” could be an excellent point of commentary. What are other examples where social orders unify, targeting one specific individual? What does it say when people in such orders behave in such a manner? What does it say when such behavior exists in America or other nations that have constitutionally safeguarded mandates designed to prevent such behavior? Another point of discussion could be in what you indicate in the subtext, in that humans follow traditions, and under what conditions should or can they break from these? Examining this might be another interesting point of commentary. I think that another point of commentary could be how the role of individual freedom is seen in such a context. Where is human freedom in such a design? I think that these might be really good areas to begin commentary and discussion.
"Commentary" is a bit vague. Are you to write a political, historical, social, philosophical, or psychological commentary? Or are you referring to literary criticism? I will answer as if you are asking about a critical commentary, a literary or textual study.
One often begins critical study by analyzing the work as a whole. What is its form or structure? In this case, you could analyze how the writer successfully concludes the story with a surprise, ghastly ending. The setting, dialogue, character actions, foreshadowing, and point of view all contribute to the surprise ending. Your task is to demonstrate how all of the above work together to create the surprise ending, and to make it legitimate once it occurs.
For instance, the setting seems completely normal. Nothing exists in the setting that would give away the surprise ending. On the contrary, the setting is exactly what one might expect. (And it is, of course, normal, which is the point: normal people are capable of great atrocities when atrocities are sanctioned by the majority.) You would need details from the story and a short quote or two to establish that the setting is normal. Then move on to dialogue, or whatever you choose to center on.
If your assignment is general, then your best bet is probably to center on the work as a whole, to demonstrate how the parts of the work form the whole of the work and make the story successful.
Using the site listed below, a reader of Shirley Jackson's "The Lottery" could tie the mindless stoning of a townsperson as a scapegoat to the actions of groups in history. Jackson's husband, literary critic Stanley Edgar Hindman wrote,
Her fierce visions of disassociations and madness, of alienation and withdrawal, of cruelty and terror, have been taken to be personal, even neurotic fantasies. Quite the reverse: They are a sensitive and faithful anatomy of our times, fitting symbols for our distressing world of the concentration camp and the bomb.
Taking this quotation, the reader can explore the dark realms of mankind that Shirley Jackson writes about in "The Lottery." The mindless following, the darkness and innate sadism in people, the fear of others that is easily ignited, the need for a scapegoat--all of these are issues in Jackson's story and issues in real history during her time that saw Nazi Germany, World War II, and the "Red Scare."
Commentary suggests opinion, but opinion based on the facts of what is read. Commentary is often thoughts that are drawn conclusions. I just wanted to make clear the premise under which I am answering this question.
One way I might start is, "If your friend was going to jump off of a bridge would you?" What I could do with this old cliche' is demonstrate how easy it is for us to do something just because everyone else is.
Another way to start might be to list a series of tasks that people conform to others on, and then ask what they have in common. Ultimately come to the conclusion that we do way too many things in our culture because other people are safely doing them.
Another attempt would be to think about the drug culture. Some kids can take hit after hit of a drug and receive the buzz, but not be hurt over the long run. Another kid can take one hit of something like meth, and because of their body chemistry and other factors, they drop dead. What a beautiful parallel to The Lottery.
Good Luck, hope this helps.