The published order of Jones' Chrestomanci novels is clear but the reading order isn't so clear cut. In my opinion it doesn't matter. They are sufficiently well crafted that it doesn't really matter, especially as one doesn't know what is going on a lot of the time anyway. Read them in whatever order you like and re-read them in whatever order you wish.
This book tells the story of the early years of Christopher Chant and has delightful characters that appear many times. Enjoy.