@PixyByte
Alil surprised by the lack of tips.
Anyway.
I've been doing freelance for 10 years, most actively for the last 3.
Find your audience. I don't recommend doing the facebook sharing with friends and family thing. That's what you do when you're doing it as a hobby. Unless your FB is full of LinkedIn people.
Your audience isn't meant to find you as much as you're meant to find them. A forum, art gallery website, etc is a good start. Its how I started. I started through GaiaOnline. I used to draw for the in game currency. It taught me about customer service without any real loss. I was in highschool, so it was fine when it went wrong or got a problem client. It also taught me how to juggle school, a job, and art at the same time.
As well, you could be networking all you want, but if you are doing it at a place that isn't as interested in your style or interests, you can't expect to find work. Do a bit of research.
Build up samples or a portfolio on what you'd like to do. Having a clear cut idea of what a client will get is best. Neither of you probably have a lot of time to discuss art "what ifs". Don't only choose your 'best work' but what you feel you can do on a day to day basis. One major flaw of some freelance artists is they offer commissions and their portfolio is all stuff they spent 20+ hours on and its their own OCs or whatnot. They won't have that much heart in something they don't own. Doing a few art trades can build a proper sample page.
Make loyal friends and fans. Not friends you already have. New ones that fell in love with your new freelance self. Never expect old friends to invest and advertise for you. They aren't getting paid. This is your job.
Be the person you want to be remembered for. Draw what you want people to remember you for. If you turn your tumblr, facebook, or whatever into your business, if you're going to post personal stuff on it, be a bit more careful. Don't annoy your watchers with spam.
Price yourself well. If you're getting a huge flood of commissions, chances are, your too cheap. If you're not getting enough, you might be too expensive. Being too cheap could also mean you don't have confidence. Its a bit of a gamble. Just average yourself on a per hour basis or what you would pay for your own quality of work. You can change prices whenever you want. Just not on someone that you're already working for. They don't like that.
Communicate with your clients. Ever buy groceries and have awkward silence for the whole transaction? Don't do that. They're spending money on art. This is a blessing to you and for them. Help them feel good about choosing you over the countless artists out there.
Create a terms of service. Don't let people cheat you out. Create a brand of yourself.
I built my audience through GaiaOnline. I then moved to two freelance forums. One was more business (like web, advertising, business card work) and the other was FAF. I get a lot of my work through Twitter now. Hashtags are important. Who you follow is important. Ask for RTs when you open for a commission type.
I make roughly 5-10k a year on commissions. I could make more, but I need breaks. I already have other work to do and freelance is part time by choice.
An artist could burn themselves out. Its also very important to keep up with in person social skills and moving around. Not making it full time has kept me from becoming unhealthy.