Other folks have touched on it here but as someone that is 5 years into a business I can tell you that no book can prepare you for what's in store. A lot of books will complement what you are currently doing, but none will even begin to tell the story of what starting a business is like.
In my experience starting up a business is a whole lot more about the psychological aspect than it is about the technical or strategic aspect. It's about being committed 100%, not just saying it, but really doing it. Leaving yourself no outs, no parachutes.
It's about getting bad beat endlessly and still getting back in the game. It's about getting put in spots that you never saw coming, and playing each of those hands as best as possible to minimize the damage.
It's about patience. Patience to see this game through. Most people don't have it. Everyone wants action. Everyone wants fast money. You have to be prepared to grind for 3 years, 5 years, 10 years, or more.
It's about managing everything outside of your business. Just like in poker, you need to be in optimal physical, mental and emotional health if you want to play your "A" game. Same with business. If your married, your wife better be on the same page. You better be efficient with your time. You better stay healthy, as you can't afford sick time.
It's about discipline. You no longer have a boss. If you slack off, you only hurt yourself. You are accountable to no one but yourself. This is hard. It takes work. Lots of work. No TV. No holidays. You will get out of this what you put into it.
You have to want it unlike anything else. No business book I have read (and I've read a lot, Ive been there) teaches this.
Ha, funny, i just realized how long it's been since I've been on 2+2. I just stumbled back on 2+2 after a 5 year hiatus. The above is what i have been doing for those 5 years.
I do have some books that I have thoroughly enjoyed. I'll post them later if I have some time. Gotta get back to the grind.