Learn about the systems that will help you succeed
If you're running an agency, I wish I found this one sooner: "Managing the Professional Service Firm" by David H. Maister - old but stands the test of time.
Awesome list Alex. Somehow I only recently heard about E-Myth but wish I had come across it much sooner. Not directly related to running a business but Steven Pressfield’s The War of Art was a beautiful and much needed slap in the face to me which I’d recommend to anyone doing their own thing. Takram’s Pendulum of Design Engineering is also a great read on how to combine multiple disciplines as an individual and as an organisation to build a greater whole. Also really enjoyed Seth Godin’s Startup School podcast series.