When I work with students on the SAT essay, many have difficulty coming up with concrete, adequate examples. Many can't get out of the quicksand of vague and directionless ideas.
Instead of ideas, let individuals from history, literature, science, and the modern era be your guides. Create a list of influential and inspiring people for each category like I've done. Focus on two or three categories you're most comfortable with and research what made these people so special and influential. Individuals such as John Proctor from "The Crucible," Abraham Lincoln, Rosa Parks, Galileo, and Nelson Mandela are just some of the examples to use when you write your essay.
SAT essay questions are broad enough that you can take something that one of these individuals has done to "advance freedom" or "challenge authority."
Remember, you only have 25 minutes. Keep calm and carry on with your "people strategy." It will pay dividends in the end.