Write the introduction, leading with your thesis statement. Briefly introduce all topics that you will discuss in the rest of the essay, but don't go into great detail. For example, you could write, "Both Macondo in 100 Years of Solitude by Gabriel Garcia Marquez and Canudos in The War of the End of the World by Mario Vargas Llosa are villages isolated from mainstream culture. They welcome eccentric people and are important for the transformation of the characters. Macondo, however, is more mysterious and magical than Canudos." You have told the reader what you'll be writing about, introduced your two points of comparison and provided the reader with your point (argument).
Write at least one paragraph about the first topic of comparison. Compare and contrast the two sources using quotes and summary. A point-by-point analysis synthesizes the source materials together in the same paragraph. A block-style analysis discusses the first source, then the second, and ends with synthesis. Develop the comparison in as many paragraphs as needed, and always begin paragraphs with a topic sentence, and stick to that topic for the whole paragraph.
Write at least one paragraph about the second topic of comparison as you did for the first topic. If you have a third (or more) topic of comparison, treat each in its own section of the essay.
Write at least one paragraph analyzing the two (or more) comparison topics you have discussed, bringing the topics together to show why both are important. You may want to introduce your own opinion of the subject and state which source was more effective, more interesting or better developed, depending on your points of comparison. Synthesize the source materials with your analysis through additional quotes or paraphrases.
Maintain parallelism throughout the essay by always talking about one work first before bringing up the second, and use clear topic sentences to ease transitions between ideas. Divide long essays into sections that treat comparisons and contrasts in greater detail, and include summaries for each section.
Write the conclusion by summarizing your argument. Restate your thesis, restate each point of comparison and summarize why those points were important to your analysis. Do not introduce any new ideas; simply bring your points together and be confident in your analysis.