I would suggest purchasing a copy of "How to Teach Piano Successfully". That's what helped me. As for the method, just choose any. Actually, choose a different method for each student that way you can experience it for yourself and then decide. Do some research on the different methods and their philosophies, then try to choose ones that are different in their approaches.
When you decide, spend time reading through each method book and creating a lesson plan for each student. Your lesson plan will change, but this is more of a guide to help you. For example, if the first lesson of a music tree book is pages 3-5, brainstorm on the different ways you can approach those pages with your student. Try to anticipate questions\difficulties (you'll get better at this).
During each lesson, take notes. And after each lesson review those notes and reflect:
- what went well
- what went wrong
- what did the student have difficulty with
- how can you explain something better
- what kind of games could you use to explain the concept
When I first started teaching, the best advice I got about choosing a piano method was to decide what I wanted to emphasis in lessons. You should do the same. Do you feel reading music is the most important or is it rhythm? Or perhaps performance? Or listening? Since there are so many methods and ways of teaching, this will help you focus as a beginning teacher.
Topic: Book and exercise recommendations for beginners