Writing is as much an opportunity to rethink your approach as it is to relate your knowledge. In most cases, your main points will change somewhat as you decide which aspects of your research to include and which to omit. As such, you should consider writing your introductory paragraph, title and thesis statement after you've completed the body of your essay. While doing so may seem counterintuitive, remember that editing one sentence is easier than limiting your entire essay to fit around a single sentence.
If you disagree with a theory or wish to posit a new variation, your thesis statement needs to acknowledge both the original theory and your interpretation. The easiest format for this sort of theory should consist of a coordinating conjunction (i.e. "while," "although," "whereas," "despite") followed by a summary of previous work, a comma, a summary of the scholarly work you agree with, and a summary of your interpretation. Be sure to reference theorists by name, particularly if you cite their work frequently within the body of your essay.
Example: "Although Foucault decried the manner whereby institutional settings robbed their inhabitants of identity during the 1960s, mass closures of mental institutions in the 1980s and the resulting high incidence of homelessness among the mentally ill suggests mental health professionals and state leaders may need to rethink the state-run asylum."
The standard five-paragraph essay usually has three main points that merge into a more or less definitive conclusion by the end. Of course, making your argument over two or three thousand words is a lot easier than making it in one sentence. Assuming you have already completed the body of your essay, read over each paragraph thoroughly to decide which aspects are most crucial to your essay. Arrange them in a series that includes a brief discussion, then paraphrase your conclusion.
Example: "The witty tone of 'The Decay of Lying' elevates Wilde's disgust with his contemporaries to that of verbal art; as such, the essay itself serves as an argument that man-made art, or the literary essay, is far superior to nature, or the disgust he feels, both aesthetically and socially."
Not only do chronological essays establish a causal relationship between events, they also let your reader know what time frame you plan to discuss. This format easily lends itself to essays in history and political science, but it can be adapted to suit nearly any discourse that deals with a specific era.
Example: "In the immediate aftermath of World War II, Japan and Germany were economically decimated, allowing the United States to assume a near-monopoly on the automobile market through the 1960s."