Before you impulsively jump into freelancing, here are some things to consider. Be very honest with yourself about each of these points. If you're still interested in freelancing, then keep reading.
1. Self Starting. If you prefer to work in groups (and preferably have someone else take the lead) then freelancing is not for you. There is no one to strike the match under you when you work alone. Projects that don't get done (or started) are lost income. If you don't do it... no one else will.
2. Disciplined. Sure, you can set your own hours, and that is real freedom. (For instance, my own preferred schedule is to rise late, check e-mail and plan my day, do errands in the afternoon, and then work fairly hard from 8 p.m. to 2 or 3 a.m.) But there's an inherent danger in not having a boss in your face: you might put off getting started so long that you never do it. You don't have the luxury of assigning out tasks to others (usually). Establishing a mode of working takes time, but once you settle on it you must, in fact, WORK.
3. Multi-taskers. It's only when you leave your corporate cocoon that you realize the true value of those great people who emptied the trash and vacuumed for you every day, and the accountants you snickered at for their lack of creativity -- but who made sure the bills were paid and taxes taken care of. Suddenly, you have to be EVERYBODY. There is no marketing and advertising department to do promotion for you. If you need office supplies, the trip to the store is on your time... and your dime. All the while you're being the entire office staff, you are also writing, interviewing, keeping track of details, filing, collecting information for another project, and capturing fleeting ideas on scraps of paper for later evaluation. They describe writing as a lonely business. A working writer, though, is generally too busy to be lonely.
4. Positive. I don't mean in the Pollyanna way, but you have to believe in yourself, your ability, and the need for your product (your writing) enough that you're willing to cut ties to security and go it alone. If you're prone to seeing the glass far less than half full, the freelance life will probably kill you.
Here are some other considerations as you warm up to that glorious moment when you cut the strings.
1. Be realistic about your benefits needs. I left a corporate PR job with fabulous, company-paid benefits. I didn't think about that as hard as I should have; my husband does not have good health, even though I'm quite healthy. Finding and paying for health insurance and other health-related costs can doom a freelancer before he or she gets the first check. If you are leaving a job with benefits, you'll have COBRA for 18 months if you elect to pay for it. Price it out in advance to see if you can afford it. And begin looking for your private insurance carrier within a month or two of going freelance. It will take you close to a year just to find what you need, apply, and get set up for it. Don't delay!
2. Consider downsizing. I don't meant your waistline, your housing. If you are going to make it in the freelance writing world, you'll be doing a lot of it online. Nobody will know your "office" is a spare bedroom in your home, if you do it right. Assume you will take a pay cut -- perhaps a steep one. Plan on that in advance. Think about moving to a less expensive home or even a cheaper area of the country. If it's got high-speed internet connection, a nearby airport (even commuter, if it connects to a major hub easily) and good phone service, anyplace can be home.
3. Never burn bridges. Many freelancers find their first client is their previous employer! Don't cheat yourself of this potential revenue source by quitting in anything but the most amicable way. Other potential clients are companies you work with or contact in the course of your corporate job already. After all, your knowledge base about your industry is a real strength -- leverage it. And realize your shelf-life on industry information is short; by the time you're out on your own a year or more, you'll be out of touch and will lose this opportunity for good.
4. Consult an accountant. Since you're now going to be the whole office staff, things like quarterly tax payments, keeping the books and financial planning will be on your shoulders. Pick up an accounting package (like QuickBooks) and then have an accountant help you set up the various categories to get you headed in the right direction from the beginning. Keep it up through the year to make tax time less of a headache. (Yes, I just went back and read that sentence five times, trying to impress it on myself!)
5. Be open to revenue streams you never considered before. I assumed when I went freelance I'd be writing articles all the time and working on my novel. Yes, I did those things, but it wasn't enough. (Nobody except the best-sellers lives on novel royalties!) I began to take on jobs that involved graphic design, which I love doing. It felt good to use more of the skills I'd acquired in my corporate job. I branched out into providing internet content. I had a client that needed me to baby sit their publication through the printing process, so I sought a local printer to do the job -- and then picked up a new client because the printer liked my work and recommended me. Don't shut your mind to types of work you "won't" do (other than morally objectionable, of course.) Follow the stepping-stones.
6. Begin planning to leave your company a year ahead of when you actually do it. Treat your freelance career like a second job all through that year -- and work just as hard at it as you would a second job. For that year, you will work tremendously hard; when you quit your primary job, it will be such a relief! You will also have confidence you can "do" the freelance thing, as you'll have been doing it for a year and seeing success. Obviously, if you have no success, you know which "job" to let go.