For beginners, my preferred method is "Piano Safari". This is an exciting, brand new method that instills the basics of piano playing in a fun context. It utilizes the entire keyboard from the very start, while other methods are stuck using five notes in the center of the keyboard indefinitley. It encourages improvisation, memorization, reading, technique, rhythm, and theory, all while playing aurally satisfying music from the first lesson.
When I began teaching, I was dissatisfied with most beginning piano methods. Too many of them focused too heavily on immediately learning to read the complicated music notation system. While reading is an essential skill, I do not believe it needs to be taught from the very beginning, as it puts too much attention on the page and not enough on the keyboard and hands. I prefer to have a period of time in the beginning where the students are focused on familiarizing themselves with the keyboard and the physical motions required to produce a beautiful sound.
For older beginners, I like to the the Hal Leonard Adult Method, or Piano Safari for the Older Beginner. It is important for me to note that the teacher is the method, not the book. I do not teach straight from any book in particular, but draw on the vast set of repertoire and exercises that are available for the piano. In this way, I can tailor my teaching to the needs and interests of each student.
I work with students as young as age five, though can teach even younger ages if there is sufficient parental commitment. For very young students (about 5-7), I recommend two weekly lessons of 30 minutes each, though I understand most parents will opt for one lesson per week. Beginning at age 8, lesson times increase to a 45-minute minimum. There are many elements that go in to making a well rounded musician, and the more time the student has with the teacher, the better!