A thesis is not a title. Ex: Homes and schools (title) vs. Parents ought to participate more in the education of their children (good thesis).
A thesis is not an announcement of the subject. Ex: My subject is the incompetence of the Supreme Court vs. The Supreme Court made a mistake when it ruled in favor of George W. Bush in the 2000 election.
A thesis is not a statement of absolute fact. Ex: Jane Austen is the author of Pride and Prejudice.
A thesis is not the whole essay. It is your main idea/claim/refutation/problem-solution expressed in a single sentence or a combination of sentences.