When you decide to freelance you need to realize you have to be a bit of a jack (or jill) of all trades. You do the work, you're your own administrative assistant, you do marketing and payroll and handle customer complaints. Freelance writing can require you to be more than just a good writer and while you might or might not be new to writing, past jobs you've had can really help you more than you might think. I used to be a sales person and a purchasing agent as well so I transfer these skills to benefit my writing career every day.
From a purchasing perspective I've learned to be very good at negotiating contracts and managing order flow. This has equipped me well for multiple deadlines and the ability to manage many clients and team members. I'm now managing a team as well and do have experience from helping to run a large call center in a previous role so those skills have come in very handy. My sales skills work well when I'm talking to new clients and writing proposals as well as helping me write persuasive copy for my clients.
My point? You might have more experience in an area than you're giving yourself credit for and you might have skills buried that you can draw on to benefit your career.
When you decide to be a writer, capitalize on all your skills to help you be a better writer. An industry you were in before might have given you enough knowledge to help you build a solid niche and net higher writing rates. Your management skills or organizational or technical skills could also benefit your career as well. Instead of looking at delving into freelancing as a foreign area figure out how to blend old skills to help you accelerate your writing career. Even if you're not new to freelancing, think about some of the old skills you have and try to put them to use today.