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.

I would look at things like the difficulties people have getting through airports, or the parts of the Patriot Act that allow eavesdropping. I'd also look at some of the examples of people who have been detained because the appear on lists, even though it turns out that they have done nothing wrong.

I would start out by saying something like, everyone knows that there are dangers today that nobody thought of several decades ago, but how far should we go in trying to protect ourselves? At what point does the issue of safety conflict with the issue of personal freedom?

First define the sides of the argument then pick a side to take. In this case there are a number of arguments/topics of argument available to you. 

• Have civil liberties actually declined since 2001? 
• Have restrictions on freedom of movement since 2001 led to a decline in civil liberties? 
• Do restrictions on freedom of movement and freedom of access effectively diminish individual liberties in an absolute way? 
• Has a national desire for safety become the more prized value compared to the desire for freedom, civil liberties, etc.? 

The first thing that you need to do is to figure out what your argument is going to be.  Looking at the things that have been done in the last 10+ years, do you think that there have been significant/excessive restrictions or not?  So, you need to gather your facts and decide what your thesis will be as a first step.