How can I begin a comparison report between a movie and a book?
When you compare two things, you are pointing out the ways in which those two things are the same and the ways in which they are different. You will add to the value and worth of your essay by also providing your analysis of how those similarities and differences contribute to or detract from the stories being presented.
To begin your comparison, you might want to present your thesis statement as a statement of your opinion; how or why did the differences between the book and the movie versions of the story add to your enjoyment of one more than the other? Then your introductory paragraph would allow you to state your observation and give a brief listing of the reasons for your position, which would then be more fully developed in the body of your report.