I run a small business that generates about 10k a month by myself. I did all of it on my own and here is what I learn.
1. The most difficult part is finding something people would pay money for. I make money off software and affiliate marketing, for example.
2. Once you have that something you know people want to pay money for, you have to build an audience. This can be done in many ways. You can join forums related to what you are selling, advertise, create a website, and more.
3. Expanding and managing your business can be challenging. Try not to change the rules of the game so much so as to not get your customers lost in new processes every time. For this, design something solid from the start.