That's a tricky one. Some things that you can do with adults really don't work with most teenage classes. For example, if you give them the answer key the worst students will copy the answers without trying first and the good students will be too shy to ask questions if they weren't sure if an answer was correct.
Learner autonomy stuff in class can work. For example, class contracts usually go down well, and discussion on the topic of how to study and learning styles is of course of interest to students. Your other main role in class is to show them books, films, TV programmes, websites etc that they will hopefully find interesting enough to use outside class.
Outside class, maybe the best thing to do is to give them open ended projects that they need to do research for.