Writing a thesis starts with research. Take a look at the primary sources you have to work with and get an idea of the angle you want to take with your paper: this will be reflected in your thesis. Since research will continue throughout the process of your paper or project, you may end up going in a different direction or being convinced your stance at the beginning was wrong. Do not be afraid to change your thesis.
The thesis tells the reader what you are planning to argue and how you are going to argue it. It not only gives a subject but makes the portion of the subject you will be arguing evident. The thesis lays out how you are going to argue your stance. Do not include your whole paper in the thesis, just the topic you will be covering and the way you will be approaching the subject. Your stance must be evident by reading the thesis.
A good thesis leaves the reader asking why or how. If your thesis is "Military service provided the best outlet for minorities to overcome racial inequalities after World War II," the reader should be asking, "How did the military provide that outlet?" or "Why did the military provide that outlet?" Your thesis provides the hook, making the reader interested in reading your argument. If the thesis is weak, the reader will say, "So what?" instead of "How?"
After writing your thesis, brainstorm the counterarguments to your stance. This directs further research and tightens your thesis as your writing progresses. Do not think the first draft of your thesis will be the final version. By anticipating the counterargument, you fine-tune your thesis to provide interest and clarify your stance.
The thesis introduces your paper to the reader. Because your thesis starts with an overall statement of your argument, you need to use clear and concise wording to bring your subject into focus. If your thesis statement is wordy, vague or hard to read, you will lose your reader's interest.