Prepare extensively for the first day of class by reading a book on communication, such as "How to Talk to Anyone"; dressing the part (wear a nice pair of black shoes, khaki pants, a black belt, and a black button-up shirt with no tie); planning exactly what you will say and do the first five seconds your students see you (the first five seconds will make up the first impression they will have of you for the rest of the semester); and planning your first lecture to impress upon them that AP chemistry is a very difficult course that will require lots of work. Fortunately for them, you are overqualified to be their teacher, and with your help, each student may succeed if he works hard enough. The amount of respect your students have for you will influence the trust they develop for the knowledge you are about to impart to them. The more trust and respect, the better they will learn.
Treat each student with respect, especially if she asks a question and even more if it is a stupid question. AP chemistry students are the brightest and most motivated students of the high school population. Treat them that way. If a student asks a stupid question, it is probably the teacher's fault, and most of the class is lost on the same point.
Prepare your lessons carefully with written lesson plans. Start by presenting the subject using as little jargon as possible. Then, give a creative real-world example that will grab the students' attention, keeping the discussion qualitative. For example, you were going to discuss the ideal gas law (P*V = n*R*T), you would begin by talking generally about how everyone has noticed some of the ways gases behave. Move on to an example of, say, putting a propane canister in a fire: "We know the increase in temperature will make the gas want to expand, but it can't. So, the pressure will increase until it explodes. If we knew more exactly how gases behave, maybe we could predict when the propane can would explode. But wait! We do know more about gases... " Then pitch the ideal gas laws, being sure to touch on the story of how they were discovered, and close the class by calculating the temperature needed to cause the can to explode using the newly learned information.
Focus on real-world qualitative ideas that guide students to the proper tools (equations) they will need to answer a certain question. A common mistake is going in the opposite direction, from equation to example. For certain areas where real-world examples aren't practical, such as when teaching how to calculate the pH of buffer solutions, help the students group the problems into categories that can be solved using the same equations. Students get lost, especially with buffers, on knowing what equation to use, not on how to use the equation.
Purchase copies of past AP chemistry exams, as well as the various AP chemistry exam test prep guides (Princeton Review, Barron's, and 5-Steps) for your students to use. Remember that their primary concern is passing the test so they get their free college credit. Your job is to enable them to do that. And, if you are lucky, you will teach them a love for learning and the beauty in science.