Without knowing what particular direction you would like the paper to take, I can only offer broad advice in terms of how to format the thesis. A thesis is generally a one sentence statement. Often, teachers like the thesis placed as the final sentence of the first paragraph. Regardless of format or placement, the thesis functions the same way. It is a statement that guides the writing process and alerts readers to what the paper is going to be about. During the writing process, always be asking yourself about whether or not the current information relates to the thesis.
As for the actual format of the thesis, you can go with two typical formats. The first is a statement/support/support/support format. The thesis will make a claim and give up to three supporting pieces of information. For example: "The Black Plague could have been avoided through better hygiene, more effective food disposal, and . . . "
The other standard thesis format is a point/counter-point statement. This format is composed of a dependent clause making one argument followed by an independent clause making a counter-argument. For example: "Although the Black Plague was devastating to human populations, some good did come as a result of it."