The response in #2 is an awesome way to get started. You may also want to compare and contrast different characters. Compare and contrast essays give you a really nice structure to follow if you are stuck. Also, enotes has a study guide for Brave New World that gives suggested essay topics.
First, pre-write. On a piece of paper, make three columns. Label them "Interesting", "Weird" and "Cool". As you reed through the book, fill in the three columns. You will start to see a trend of related ideas. Figure out what the trend has in common and make that the basis of your thesis statement.
Start with the basic statement: "A Brave New World is about ___." Once you fill in the blank, come up with three arguments (they will be on your pre-write) that explain how you know this. This will give you a good start.