There are many books and manifestos or even books about those manifestos :-) the aim of which is to teach you how to be more efficient. They provide you with diverse recipes and tools to be more efficient as a person, as a developer but also as organizations.
All those writings also have another important thing in common; they all say that in order to be more efficient you constantly need to focus on delivering value or even steadily adding value.
I did a presentation during a Paris Software Craftsmanship Meetup, where I tried to define what exactly value is and the kind of things you could put in place (and things to avoid!) to bring it down to your code or even within your tests.
Here you go!