The Effective Executive by Peter Drucker
Every manager should read Drucker, and The Effective Executive is the best place to start. You'll find the dated references because he was writing this so long ago, but the general principles still stand.
You'll find that the things Drucker talks about are the basics of my program and what I believe. I've adapted it a bit for modern times and for some things we learned from data and research.
One warning: It is dense with information and can be a difficult read. Don't be surprised that you have to read certain passages multiple times. Drucker crams a ton of information in as few words as possible, which requires deep reading. This is not a beach book. This is one that will require multiple highlighters.