The first skill is empathy. The ability to imagine why other people do what they do. This is extremely hard, especially for smart people, because our tendency is not to empathize, but to evaluate. We may ask, "Why did you do that?" but really we are saying, "How could you do that?" There's no good reason for it!
In business, however, your job is not to judge. It's to understand. Your first question is, "What is my customer trying to do?" What are they trying to have for themselves? What internal need are they trying to satisfy for themselves?
I say the word "trying," but truth is, people are rarely aware of what they are trying to do. But you must be.
The second skill is problem-solving. This is easy enough to understand. Your role as a business is to let people do what they are trying, but don't know how, to do. This means you have to have the know-how, the skills, to allow them to do what they can't do, or would rather not do, by themselves.
Even more, you have to provide a solution that is sustainable. Meaning that it is cost-effective for you to provide. This is sustainable because the more cost-effective for you, the more cost-effective for your customers (another solution).
The last skill is communication. It's not enough to solve people's problems. You have to communicate with people that you have the solution to the problems they are having. They have to be able to see very clearly that your solution solves their problem.
There are 3 forms of communication this can take: verbal (spoken, written), visual (video, pictures), and kinesthetic-tactile (feeling and using). The best form is kinesthetic-tactile, the next best is visual, and the third best is verbal. Either way, the goal is to communicate to the customer: "This is for you!!"
With these three skills, you have the foundation for running a successful business. Without these skills, you have a foundation for failure.
Of the three, I'd say empathy is probably the most important to develop, so I'd start there.