Some of the stuff I recommend and use in my approach to work and life in general:

Sales and customer focus
Robert Cialdini, Influence. The power of persuasion
(very good to understand principles of persuasion)

Lean and systems thinking
Jeffrey Liker, The Toyota Way
(about Toyota’s lean approach)
John Bicheno, The lean Toolbox/The Service Systems Toolbox
(about lean tools)

Francisco Varela, Ethical Know-How. Action, Wisdom, and Cognition
(about life and systems thinking)
Quentin Skinner, The Foundations of Modern Political Thought
(on the historicity of our political-philosophical discourse)
James Carse, Infinite and Finite Games
(about life and games)
Viktor Frankl, Man’s search for meaning
(about life)
Josef Pieper, Das Viergespann
(about the virtue ethic)

John Gottman, The seven principles of highly effective marriages
(about effective partnering, includes exercises)
Harville Hendrix, Getting the love you want
(about attachment, includes exercises)
David Schnarch,
(about individuation)

Calvin and Hobbes
(on life and curiosity)
(on organisational life and logic)
Le petit Nicolas
(on innocence and mild humor)
Van Kooten en De Bie
(on life’s characters)

Alexander Solzhenitsyn, One Day in the Life of Ivan Denisovich
(about life and mindful eating)
Erich Maria Remarque, Im Westen nichts Neues (All quiet on the western front)
(about the horror of war)
Junichiro Tanizaki, The key
(about the human mind and emotions)