"Freelancer" is such a generic term, right up there with "Contractor" or "Consultant" for telling people absolutely nothing about what you actually do.
As many people would be happy to tell you, the term "Freelance" comes from "Free Lance," basically a lance (mercenary) for hire rather than belonging to this or that noble's guards or army. This definition leads to all kinds of jokes about cut-throat industries, etc., but it's basically accurate. A freelancer is self-employed, moving from one job to another as time and work dictate. At any given time a freelancer may be working solely for one client, or for many clients at once. The next day, they may have moved on. The next year, they may still be working for the same people.
Some might say that those who prefer freelance have commitment issues. Personally, I turn around and point out how the corporate world no longer holds any promise of actually keeping the same people employed until retirement. It's companies trying to cut corners and costs that have commitment issues as well. There's no guarantees that you'll be working in the same place tomorrow no matter who you work for, so really the ability to handle self-employment even in the short term is a good survival skill for anyone to have.
One thing you are guaranteed, however, is that freelancing offers an unparalleled chance for variety. Now, by variety I don't mean constantly doing wildly different things. Surviving as a freelancer involves making a name for yourself, and to do so you generally need to specialize in something. There are many ways to approach this specialization. In my case, most of my career has focused around Linux and open source. I've written around 15 books, over 300 articles, a couple of radio appearances, some TV appearances, and more than a half dozen courses on this set of topics. I've presented workshops at conferences, done corporate training, and taught classes online, all mostly (but not entirely) within the sphere of these areas.
How do I manage this variety without completely losing track of things? I've chosen a set of delivery methods around my specialty that are all side-steps. Writing, training, and course development are all closely related fields. Interviewing movers and shakers in the community and writing how-tos both lead to articles of different types, but yet both can center around the same specialty (Linux and open source). I have variety so for one thing, I don't get bored (which unfortunately is easy for me to do), and for another, I have multiple avenues for making a living. Sometimes articles are hard to come by. Sometimes there aren't a lot of books to be had. Or business cycles mean that sometimes companies are dying for training and at other times they have higher priorities. So whenever I want to try something new, I ponder what else out there is a step to the left (no this doesn't refer to politics) from what I'm already doing. Look at what you already know, and leverage it.
That said, sometimes times call for a step to the (non-political) right. Maybe I want to write or teach about another topic. For example, I've had dogs for 12 yrs and really enjoy working with them. Or I've done stained glass and mosaics and even sold some pieces. I've sold some fiction in the past as well. Even if I don't have a name in another field, I can at least approach potential clients and demonstrate that I have a solid track record of delivering good work on time in another area. Having that background makes it more likely that they'll give me a chance, though expecting to be treated like an expert or one of their regulars is another matter all together. A step out of your specialty generally needs some humility to do gracefully.
So there you have it. In a nutshell, freelance survival means specializing around a topic and then finding enough ways to deliver your expertise around that topic so that you have enough work to make a living. From there, when you hunger for a change, you can leverage the skills you have to try to break into another topic, as long as you remember that you'll have to pay your dues somewhat again before you rise to be a known expert there as well.