Take advantage of your students' energy level and don't ever let them shut up. Organize them in small groups and release a thousand communicative activities on them. As long as your students are speaking in the target language, stand back and enjoy being a professional educator, monitoring your students for possible linguistic errors.
Discipline-wise, why not carry a stick to class? For the age level you are describing, chances are that you will walk into a classroom full of rebellious teenagers that want nothing more than to run all over you. Don't ever put yourself in that position! From the first day of class, demand respect from your students. You are their elder and are a subject matter expert, right? Adolescents are looking for direction. Be their lighthouse and teach them how to be a positive force in a global society.
Try inviting one of your students' parents to be a guest speaker in your classroom. If he or she says great things about you in front of your students, your discipline problems will cease to exist. The more that you can involve the parents (letters, e-mail, instant messaging, audio and video conferencing) in your classroom, the easier your job will be for the rest of your life.
Speak softly because their should never be a need to raise your voice to someone that is willing to learn.