ROBIN'S LAW: OF GOOD GM'ING
This book is a worthwhile read for those looking for sound, fundamental principles of Gamemastery and practical advise for improving at the same. For some (especially advanced gamemasters), much of the information contained within may be very familiar. However, there will likely be a few "that makes sense, I understood it on some level, but never would have thought of describing it that way..." moments. Even 30-year veterans of the gamemastery trenches should be able to appreciate the collected wisdom this book offers; this is likely the book you wished you had way back then, when you started.