Before your first lesson, I recommend you purchase some of the following books as these will be the materials I will use. If you teach yourself, then these books are good as well but for a more rounded musical education, I do encourage you get some lessons.
The Complete Piano Player (Books 1-3) For Adults
This series of tuition books have been around for a long time and is a little dated now in its presentation. Despite this, all the books in this series are presented in a logical order, rightly focusing on hand positioning, posture and technique early on. It gradually introduces new notes, with the first one you learn being Middle C. The way new notes are introduced encourages sight reading and watching out for the finer detail such as articulation and dynamics. These books mainly consists of popular music from the 60's and 70's and has been designed with the adult beginner in mind so therefore don't recommend this for younger learners
John Thompson's Easiest Piano Course (Books 1-2) For Children age 6 - 8
Trying to keep young ones engaged in lessons can be a challenge and I have tried many different books, methods and games. However the one I keep coming back to which strikes a nice balance of educating young ones music while keeping the lessons fun is this series of books from John Thompson. It introduces only one musical element at a time, the music notes are large and easy to identify. There is also an accompaniment for the teacher to help enhance the learning of new tunes. Various animated characters appear throughout the book to help young ones learn new musical concepts. While not every tune is familiar, some of them are known. There is also a certificate waiting to be signed at the back of the book. It certainly encourages musical progress.