To compare is to explain the similarities between two subjects. To contrast is to explain the differences between two subjects. These similarities and differences will become the main ideas of your body paragraphs. When choosing which similarities and differences to discuss in your essay, be sure they are significant or thought-provoking. The goal of your essay should be to leave the reader with a new outlook on your subjects, not to tell them information they already know.
Despite which method or organization you use, the order of your main points is the same: your strongest point comes last, your second strongest point comes first, and your weakest point goes in the middle. So, if you are using the point-by-point method, arrange your paragraphs with your strongest point in the third body paragraph, your second strongest point in the first body paragraph, and your weakest point in the second body paragraph. If you are using the block method, place your strongest point as the last main idea in the body paragraph, the second strongest point as the first main idea, and the weakest point in the middle of the body paragraph. The reasoning behind this is simple. You are sandwiching your weakest point between the two strongest points so that your essay is compelling at the beginning and at the end.