There are different structures you can use for your essay paper.
The alternating method is where you look for a point-by-point pattern. The main subjects for your paper are A and B and in this method you alternate between the two. For example: if you are writing a comparative paper on the American revolution and the Mexican revolution you might want to review the way that new technology as well as military strategy and administrative systems either encouraged innovation for the revolution or hindered it. In this case your paper might follow the structure below:
Paragraph 1 in body
new technology in the American Revolution
Paragraph 2 in body
new technology in the Mexican Revolution
Paragraph 3 in body
military strategy for the American Revolution
Paragraph 4 in body
military strategy for the Mexican Revolution
Paragraph 5 in body
administrative systems in the American Revolution
Paragraph 6 in body
administrative systems in the Mexican Revolution
Take heed that in the example above the subjects A and B may be dissimilar. You do not have to say how they were similar but only how they were noteworthy. It is also best to include three or more pairs when you are writing with the alternating point method because it gives your reader enough content to understand your subject matter.
Many professors prefer this method because it highlights the differences and similarities better. It also offers a more analytical and tightly integrated paper more often than not. If you can clearly identify the points between subjects A and B then this method of organization is best.
You can use the block method to write a paper that follows a subject-by-subject pattern. In this method you will write all about subject A and then write all about subject B. So if you are using the American Revolution compared to the Mexican Revolution you will present the American Revolution in the first half of the paper and the Mexican Revolution in the second half. This technique allows for higher continuity and cohesion within your paper. If you use this method of organization it would look like this:
Paragraphs 1–3 in the body of your text
How the American Revolution either encouraged or thwarted innovation
Paragraphs 4–6 in the body of your text
How the Mexican Revolution either encouraged or thwarted innovation
This method is useful in cases where you ideas about subject B need to expound upon the ideas related to subject A or when you are comparing three or more items. It can also be used if you cannot find points about the two subjects which are closely related.