How to become a good freelancer writer?

I think for most of the tips here can be applied to almost every writer.
Read: Have a good reading habit. It helps you identify effective writing styles and how you can corporate that into your own style. You should read articles, books, blogs,… they make your more aware of the topics you trying to write. My suggestion is just chosen a niche and stick to it.
Start writing: You have to actually write to be good at it.
Researching skill: this is a requirement. The important skill you need to master. A good content should be well research and should give the right solutions and information to readers.
Build a portfolio:  Employer will usually need proof on your work and skills. There is no better way for them to do that than a portfolio.
Don’t give up: Freelancer writing can be quite challenging. There will be a time when you will feel discouraged, just keep in mind to stay persistent. It will take a while for you to an actual project that pays well.
I hope these tips help you. Good luck.