Plan B: Use Plan B if you have only a few, larger similarities or differences. After your introduction, in the next paragraph discuss one similarity or difference in BOTH works or characters, and then move on in the next paragraph to the second similarity or difference in both, then the third, and so forth, until you're done. If you are doing both similarities and differences, juggle them on scrap paper so that in each part you put the less important first ("X and Y are both alike in their social positions . ."), followed by the more important ("but X is much more aware of the dangers of his position than is Y"). In this format, the comparing or contrasting goes on in EACH of the middle parts.
Essays are structured around an introduction, body and conclusion, and the text itself is separated into paragraphs. See examples of the more formalised components of the essay, the introduction and the conclusion, in What does a good introduction look like? and What does a good conclusion look like?. The structure of an essay is not as formalised as that of a report. In some ways, you have more discretion about how you put your essay together, although you need to adhere to disciplinary expectations. Like reports, however, you must still provide an argument or position that is clearly sustained; that is, your reader must be able to follow what you have written. Refer to 'The reader – the writer' in How can I improve my argument? for more on this.