In order to put your preparation to use and take the AP English Exam in May, you will need to ensure that you are registered for the exam within the next few weeks. Different students will have to take different steps to become registered for the AP English Exam.
If you are enrolled in an AP English Course at your school or at least go to a school with AP courses, your school will have an AP coordinator who is in charge of registering students for exams. That person's job is to make your life easier, at least when it comes to getting your paperwork in order to take the AP exam.
If you are actually in an AP English course, you can expect your teacher to bring exam registration materials to class (if (s)he hasn't already) for you. If you're not in an AP English course but your school offers AP courses, ask someone to direct you to the AP coordinator. The coordinator will be able to provide you materials for exam registration.
If your school does not offer any AP courses, or if you are home-schooled, but you are still preparing for the AP English Exam and want to register, you will have to take some initiative. Before March 1, you need to call AP Services at 888-225-5427. Someone at this service line will help you find a school in your area that allows outside students to come in for AP tests. You will receive contact information for the AP coordinator at that school, and will need to reach out and arrange things with that AP coordinator.
For the details of this process (including the upcoming deadlines for taking these steps) see the College Board website: http://www.collegeboard.com/student/testing/ap/reg.html.
It's important to make sure that you have your AP English Exam registration taken care of, or else all your other preparation will go to waste. If you have any questions about this process that haven't been answered here, find an AP coordinator to talk with, either at your school or in your area. These people are trained to help students organize AP testing, so they can check for you that you are signed up and ready for your AP exam.