Besides, you have to learn: planning, business, geomantic omen, architecture, planning, design and other aspects (it is good to know, you don't need to be very professional).
Finally, there are some books about mentality, such as: The Greatest Salesman in the World, Letter to Brazil, Sold Out and so on.
. . . . . . Anyway, a lot, enough for you to learn slowly and make progress slowly!
The content of the book is about sales skills, dealing with people and so on. You will understand after reading it.
I hope it helps you, and I wish you success.