I wanted to get in touch with this topic and starting with principles certainly did not look like a bad idea(to me). I enjoyed reading those principles told in short practical stories, that made it more human digestible. I also appreciated that the references are indicated directly on the same page, it's silly but it makes a world of difference in my reading.  

Don't read this if you don't care about human interaction and if you don't want to hear about Daniele's life events !  

I have read a book a long time ago, Raving Fans written by Ken Blanchard and Sheldon Bowles that focused more on customer service and in a way, it complements what I've read here by helping you defining your limits when designing your (customer) service.