Whether or not you've tried freelancing before, the idea of "freelance writing" probably conjures up a particular type of writing for you. Maybe you're picturing writing for magazines, or writing advertising copy, for instance.
There are lots of different types of freelance writing out there, though -- and this isn't an exhaustive list, just a look at some key possibilities:
#1: Freelance Blogging
This is where I've chosen to focus as a freelancer: writing pieces varying from 500 words to 3000 words or more for websites that have a blog. (They don't all call it a blog: it might be an "online magazine" or an "articles" section.)
If this is the route you go for, you'll want to have a fair degree of comfort and ability with techy things and, ideally, some experience with WordPress (almost all the sites I work for use WordPress).
#2: Freelance Article Writing
If you want to write for magazines or newspapers, you'll likely be writing articles of some sort. These could have a similar wordcount range to blog posts: a short column might be 500 words, whereas a long article might be 8,000 words or even more.
Pay varies a lot depending on the publication: a tiny local paper might not be able to offer anything other than expenses; a well-known national publication might pay hundreds of pounds or dollars. You'll need to be comfortable with interviewing people (as many articles are built around interviews and quotes from experts).
#3: Copywriting
Copywriters produce marketing and sales "copy". That means things like advertisements (print and online), sales pages for products/services (sometimes called "landing pages" on the internet), and marketing emails. As well as being a competent, fluent writer, you'll need a great understanding of how to write persuasively to encourage people to buy.
It'll help if you've had some experience of marketing and/or sales, though there are plenty of courses you can take on copywriting. If you want to write B2B (business to business) promotional material, you'll likely need a strong grasp of the industries in question and the type of language they use.
#5: Technical Writing
Technical writing involves writing instructions of some sort. I did this in my (long ago) day job, where I worked in IT, writing user documentation. It can seem a little "dry" but may well pay better than other types of writing -- and if you have expertise in a particular area, it can be a great way to make a living writing.
You'll need the ability to explain processes clearly, especially if you're writing instructions for people who aren't experts.
#5: Ghostwriting
Ghostwriting means writing for someone else, who'll publish your work under their name. It's perfectly legal, and it can be done in any of the above areas -- though you can also freelance as a ghostwriter on full-length books, both fiction and non-fiction, if you have the appropriate skills and experience. (With copywriting and technical writing, note that you often won't get your name on the finished piece anyway.)
Quite a bit of the work I currently do is ghostwriting, and I enjoy it because it's a chance to write things that don't necessarily fit with my own "brand" as a freelancer.
Of course, there are other paths you might go down as a freelancer, particularly if you want to branch out from purely writing. You could edit other people's work (the rise in self-publishing means there's plenty of work out there for novel manuscript beta readers and editors), or go into proofreading. Alternatively, you might specialise in an area like social media, where you're combining writing with marketing and technical
skills.
Freelance writing can take lots of very different forms. Whatever type of writing you enjoy, and whatever other skills you have, there's almost certainly a type of freelancing that would be a great fit for you.