...ask yourself a genuine, difficult question about the topic (usually a “how” or “why” question), and state your response, even if you are not sure why you want to give that answer. Your response may very well be a workable thesis, and the pursuit of proving that answer may reveal to you more about your sources of evidence.
...think of a strong statement or observation you have made about the subject beginning with the words “In this essay, I will...” Then ask yourself why this observation is important, or “So What?”1 Answer the question with “I believe this is because...” In the draft stage you might phrase a working thesis as the following:
In this essay, I plan to explain how Mark Twain’s Adventures of Huckleberry Finn contrasts his river and shore scenes. I believe Twain is telling us that in order to find America’s true democratic ideals one must leave “civilized” society (the shore) and go back to nature (the river).
Then revise out the “I” statements. A revised version of this thesis might look like this:
Through its contrasting river and shore scenes, Mark Twain’s Adventure’s of Huckleberry Finn suggests that to find the true expression of American democratic ideals, one must leave “civilized” society and go back to nature.
Keep in mind that thesis statements vary depending on the purpose of the assignment (or type of essay), and also by discipline. Here are a few notes on the thesis statements and the purpose of writing in a few different disciplines.2
English: “A thesis is an interpretive argument about a text or an aspect of a text. An interpretive argument is defined as one that makes a reasonable but contestable claim about a text; in other words, it is an opinion about a text that can be supported with textual evidence."
Sciences (Biology): “A well-written scientific paper explains the scientist’s motivation for doing an experiment, the experimental design and execution, and the meaning of the results... The last sentences of the introduction should be a statement of objectives and a statement of hypotheses.”
Business: “When you write in business courses, you will usually write for a specific audience. Your goal will be to communicate in a straight-forward manner and with a clear purpose."3
History: “In historical writing, a thesis explains the words or deeds of people in the past. It shows cause and effect; it answers the question why?... A thesis must change a reader’s mind to be of value. If it presents only facts or an obvious finding, it will merely confirm what the reader already believes.”
1. This strategy comes from Writing Analytically by Jill Stephen and David Rosenwasser.
2. The following statements on writing in the disciplines have been borrowed from the Writing Guides found at the Writing Across the Curriculum website at http://wac.gmu.edu/guides/GMU%20guides.html.
3. From A Writer’s Reference, 6th Edition, with Writing in the Disciplines, by Diana Hacker.