The first sentence of any paper is important, and the thesis paragraph of a research or thesis paper is no exception. Readers need to be caught by what you are saying and they need to understand what the paper is about in the first sentence. Make sure that sentence one says what the subject is and how you plan to write about it.
The second sentence is there to support the first one. Re-write the statement announced in the first sentence, but make it slightly broader, mention sources that might be used in the defense of the subject or in backing your claim.
The paragraph continues to expand in the third sentence. In sentence three, you can further widen the claim or defense by telling what techniques you will use to defend yourself. The reader should be able to see what is going to be found in every paragraph at this point.
The final sentence of the thesis paragraph is the thesis statement. This is not only the most important sentence in the paragraph, but it is the most important sentence in the essay as a whole. The statement should offer a concise claim or defense. It should say what the essay is about, but this sentence is different from the first sentence in that instead of presenting generalities it should hone in on specifics about how you will defend your position.