I applaud your desire to be a great freelance marketer. It is an exciting and fulfilling career choice!
This answer has many parts, mainly because running a freelance business has many facets.
You will want to take some basic business courses to understand how you should operate your business. This will cover accounting, client communication, organizational flow, etc.
You will want to take some basic marketing course to understand how to get more clients as a freelance marketer. This will cover using your website, social media, and your professional portfolio to attract new and high-paying clients.
You will want to take some courses that are specific to your service. Marketing for example is a huge industry, are you considering a niche? A specific industry or product?
Also, you will want to understand this idea of “work-life balance”. Often, we blur the lines between work and home because we do not do a good job of maintaining those boundaries (for a number of reasons). I would argue that this consideration is also a quality of being a good freelancer.
Obviously there is a lot to consider. I’d be happy to help and clarify, if you have specific questions.
All the best,