Write a basic plot outline of the story for your essay. Include every action the characters take that affects the plot and every point of conflict. Conflict can be between characters, within characters (self-conflict), or with nature or the world in general.
Decide what you want your essay to focus on within this plot. A plot essay can be a study of one character's actions and how he caused the outcome of the story, or a study of how the characters overcame all of the obstacles that stood in their way. You could study the plot from the angle of the protagonist, who has a goal and strives throughout the story to achieve it, or from the angle of the antagonist, who's goal is to stop the protagonist and how he does so.
Write an outline for your plot essay. Include an introduction and conclusion, as well as three to five points of study. For each point, include not only a description of what happened in the plot, but tailor it to the focus you chose in Step 2. Was this a character vs. character or character vs. self conflict? How did it affect the outcome, or the antagonist? Study each point from all angles to tie your points together cohesively.
Write an introduction to your essay. Open with an attention-grabbing sentence, such as a powerful quote from the story, then follow with an explanation of the focus of your essay. Inform the reader in exactly which way you are criticizing or analyzing the plot.
Write a paragraph for each point in your outline, expanding on the ideas you wrote in Step 3. Allow yourself to make new connections and ramble a little bit, as you will go back later to revise and edit your essay.
Write the conclusion for your plot essay, summarizing the connections you made and explaining the conclusions you came to based on your study.
Read your essay all the way through, making notes in places you think need improvement. Ask yourself if the essay stayed clearly focused on the angle you chose throughout, and if each sentence is in some way related to the plot of the story you are studying. Revise and edit as necessary.