Depending on what exactly the question is, I think it is very important that you determine your stand before you write. Is the question ARE there greater restrictions to civil liberties since 9/11 or are the restrictions OK? These are two very different questions. The first would involve more research into new laws (Patriot Act) regulations and practices ( creation of Department of Homeland Security, travel policies, etc). The second is about persuading your reader that these laws regulations and practices are either hurtful or beneficial. The question is which trumphs, security or personal freedom? How much freedom are you willing to give up to be/feell secure? Does losing some freedom even ensure your security?
In any persuasive essay it is important to state your side in the very first paragraph then use details and examples to support your side. The worst thing you can do in a persuasive essay is be wishy-washy. State your side outright at the very beginning and only use examples that support that view.