If you're interested in my book, the link is in my profile; it has practical tips specifically for freelance programmers/developers/consultants/coders/software engineering people. But if you are purely interested in improving your business skills, then I recommend reading "The Personal MBA" by Josh Kaufman.

Also, I'm a developer but my father is a Silicon Valley business lawyer. He wrote a chapter of "The Software Engineer's Guide to Freelance Consulting" that is available for free. https://codefor.cash/legalideas