What I'll do to help answer your question is outline the ideal structure of an introductory paragraph and then correlate it specifically to your prompt:
Hook: The opening line of an introduction paragraph should be one that "hooks" your readers' interest in the overall themes or arguments found in your paragraph. A hook could be a question, a quotation, a statistic, a hyperbolic claim, or another attention-grabbing sentence. Given that your essay addresses the ways in which Steinbeck uses his characters to illustrate and comment on "good" and "bad" people, I would encourage you to focus on that theme: what makes someone good or bad?
TAG: A crucial element for your introduction paragraph is to provide your readers with literary context: the title, author, and genre of the work in question. For your purposes, you want to make sure that your intro. paragraph reveals that you will be discussing John Steinbeck's novella Of Mice and Men.
Context: You'll want to take a moment to offer a brief overview of the ideas that your essay will touch upon. This is different than providing a preview of your argument; it is more important for your readers to understand the types of ideas that they will be reading about than to know about the order of paragraphs in your essay. As I don't know what your essay is going to argue, I can't provide much guidance here.
Thesis Statement: A solid introduction paragraph ends with a definitive argument. Keep in mind that your argument is not about which characters are good and which characters are bad, but that it should be an argument that seeks to explain how Steinbeck illustrates characters as good and/or bad.