When writing an essay on the theme appearances can be deceiving, how would you start your opening paragraph?
What about the scene from the final chapter as Scout stands on the Radley porch and realizes that looking from another's perspective can alter one's perception of reality:
I turned to go home. Street lights winked down the street all the way to town. I had never seen our neighborhood from this angle....
Atticus was right. One time he said you never really now a man until you stand in his shoes and walk around in them. Just standing on the Radley porch was enough.
How about the opening lines, which are spoken by Scout at the beginning of the novel, starting with
"Maycomb was a old town, but it was a tired old town when I knew it."
This description is accurate, of course, but it has no hint of the underlying racism and gossip and ugliness OR the generosity and justice and humor which we will soon see. In other words, Maycomb "ain't just what it appears to be." Happy writing!
You might consider using the last few pages of the book. Scout was falling asleep as Atticus was reading to her. The book was called The Gray Ghost. There was a character named Stoner's boy who everyone thought kept messing up their clubhouse. Scout is barely awake, but she tells Atticus that it wasn't really him at all, it's just who everyone else thought was doing it.
After bringing up that situation or summarizing it, you might transition into a nice sentence that states how similar this situation was to people's perceptions of the real characters in To Kill a Mockingbird. Then write a thesis that outlines your paragraphs with one being about Boo, one about Tom Robinson, and maybe one about Atticus.