The most important thing you need to be an AP teacher (besides a position that needs to be filled in your school) is evidence that you are the most qualified candidate for the job. Enthusiasm for the subject matter, being well-read, having excellent student-teacher relationships, and having enough time and energy are some of the things that an administration would be looking for. It is a very public position to have -- the scores the student's achieve are a measure of what happened in your class, so you have to be ready for that aspect of teaching AP as well. The students can be the most fun but most demanding. Teaching AP has certainly made me a better teacher.
Teachers must be certified to teach English classes at the high school level. The class syllabus must be approved and your district has to request and be approved to offer AP courses.
In our local districts, qualified teachers may teach AP classes if they have a strong background in the subject area. Sometimes teaching these course is need based. In addition, our area high schools have dual enrollment high school/college credit, but these teachers are required to have a masters degree.
I work for the College Board in addition to teaching high school. Anyone can teach AP courses if you are qualified to teach the regular courses. If your school already has been accredited to have AP courses, you'll just need to submit your syllabus for the audit. Follow the link below to the College Board website for AP for info on the curriculum, the test, and submitting the syllabus for the audit. They have samples there.
If possible, try to get your school to pay for at least a weekend workshop, taught by College Board employees like myself who have taught the subject for a number of years. There you will get teaching ideas, materials, and advice on how to approach a new course offering. If possible, get to a weeklong seminar in the summer. Professional development credits are usually available.
On the AP website, there are links to English Literature and English Composition, whichever you are more interested in.
Generally speaking, school district administration or site principals select teachers to be trained. You cannot teach any AP class without having gone through the training.
I believe the process is a week or two during the summer and there is a fee that school districts generally assume. There is one training in LA this summer. You might google the College Board.
I would encourage you to go speak with your principal about the potential for you as a teacher to do so.
One certification you can seek on your own for the prestige in the field is National Board Certification. Check out nbpts.org.
go to AP CENTRAL
you will have to apply and make a syllabus and everything...check with your school...there may be workshops in the area where you can get a head start.