If you want to understand the business world, the management aspect of it, I suggest reading Peter Drucker's Management: Tasks, Responsibilities, Practices.
If you want to get better at networking, I would suggest reading Dale Carnegie's How to Win Friends and Influence People.
If you want to understand marketing, I would suggest, Marketing: An Introduction by Philip Kotler
Peter Thiels' book Zero to One might be a good starting point to understand the start-up world.
But for a general instinct about business, you have to stay curious and learn how people think and behave. Being curious about anthropology, psychology, economics, news, trends, sociology are key.