If you have a firm understanding of the material, well-selected evidence, and a strong thesis, your conclusion should write itself. In other words, the conclusion summarizes what the essay argues or sets out to demonstrate. Ultimately, the quality of your essay is measured by whether or not the reader is persuaded by your thesis and how well you supported it. And then revise again. Then revise some more, just in case you missed something.
Revision is the process of finishing the essay.
Take pride in your work by making sure there are no obvious erors in it. Because revising your work takes time, you will need to plan ahead and compose the first draft of your paper before any deadline. Seek help from others in revising your essay. Although it is important that your essay be your own work, there is nothing wrong with asking someone else to read over your first draft and make appropriate suggestions on improving it. This is one of the main jobs of the tutors here at the History Tutoring Center.