It is important to do enough preliminary reading about your topic that you have a basic understanding of the various issues, key concepts, and facts associated with it. There is no substitute for doing some initial investigation of your topic. The more background information you have, the more effectively you will be able to focus the topic. Based on your focal points and how they relate to each other, you then form a thesis statement for your research.
A thesis statement is usually one or two complete sentences describing the precise question or issue you will discuss in your paper. It can be a debatable point that requires you take a stand and defend your position or a claim that needs explanations and evidences. You need to develop your arguments in response to the How? Why? and What? questions prompted by your thesis statement. The thesis statement, which often appears at the end of the first or second paragraph, should be specific, covering only what you will discuss in your paper. Remember that your professor is a valuable resource as you attempt to formulate hypotheses and research questions.
For further information, consult the helpful guide, “Tips and Examples for Writing Thesis Statements" from the Online Writing Lab at Purdue.