A thesis statement is a statement of purpose. It will guide the rest of the paper. In fact, it guides it so much so that each following paragraph should reflect back to the thesis in some way. If that paragraph doesn't do that, it doesn't belong in the paper. Traditionally, your thesis statement should be the last sentence of your introductory paragraph. It's not always there, but teachers expect students to put it there.
I teach my students two standard thesis forms. The first form is the "statement-reasons" format. If you use this format, your thesis will make a statement of some kind followed by 2-3 reasons why you think that. For Francisco Jimenez, you could have a thesis that goes something like this: "Francisco Jimenez's books have received critical acclaim because he writes from personal experiences and about characters that minorities can relate to."
The second thesis form uses the word "although" to begin a dependent clause. Using this format forces your thesis to be a compare and contrast thesis. The dependent clause says one thing, and the following independent clause shows a "better" opinion. "Although Francisco Jiminez's books are about fictional characters, they reflect the struggles of immigrants in stunning detail." That thesis will let you discuss his books, his characters, and his life as an author.
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