Make notes as you read. There will be ideas that come to you while you're reading that you may forget by the end of the book. Making notes regarding the way you feel about the opening of the book, characters and the overall story can be helpful when it comes time to start your book report. Having notes written in the order thoughts occur to you can help you formulate a more cohesive opening for your book report, as well as a general focus for the rest of the report.
Begin your book report by stating the title of the novel and the name of the author. An introductory line such as, "Tom Sawyer by Mark Twain is the story of a boy . . ." This introduction gives basic information about the book and leads into the next section of your book report.
Introduce the book's main characters and setting in the first paragraph, immediately following the book's title and author. Use two or three paragraphs to discuss this information. You could start with something along these lines: "Tom Sawyer by Samuel Clemens is the story of a boy growing up in a small Midwestern town who finds himself center stage in a mystery . . ." Again, this is basic information that helps lay the groundwork for the rest of your book report.
Continue to build your book report from the opening you've written, as well as the notes you took while reading the book. Provide greater detail about the story by addressing some of the major plot points, including obstacles the main character faces or important decision he or she makes. Devote several paragraphs to discussing these details, then end your book report with a paragraph summing up your thoughts about your overall enjoyment of the book.