@ Adam:
Full-time job? Human resources clerk. Rather low pay, but has nice benefits.
Hmmm... I started by posting a price list on my deviantArt journal, showing what I'm capable of and the prices for the different complexities of art (simple portrait with plain background, all the way up to a full multiple-character action illustration). I then go around working on my own work and submitting them to the relevant groups to showcase my work, as a form of "advertising".
Eventually someone approaches me for a commission, where we work out the subject matter and therefore the price. Client pays the agreed price (paid in full for anything below $20 USD, more than that can be paid in instalments according to the work progression), usually through Paypal for international, or a bank transfer if the client is Malaysian. I then work on the art, submitting the necessary WIPs through e-mail for approval and to check with the client that the art is according to their specifications. I try to get as much detail about the work as possible before even starting, so I don't have to make corrections, but inevitably there are times where the client changes their mind or I simply deviate a little too much from the client's "vision", so I have to be ready to make changes if necessary.
Once the art is done, I send the signed, full-resolution copy to the client through e-mail, and then I submit the low-res, watermarked image to deviantArt, so I build up my portfolio of completed, commissioned works that way, and start the process of building exposure through groups again.

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@ acefreakz
Let's just say that I've been in a very, VERY dark, bleak place in life before. The sort of dark place that involves sitting on the edge of a very high bridge over a very deep river, and wondering about life expectancies. The art is pretty much the only thing keeping me from going back to that particular path over the bridge again, so I'm lucky to actually discover that I enjoy it. Otherwise you wouldn't be talking to me right now
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@ Agito
Can't say I'm very good yet. Just extremely stubborn about improvement, I suppose. Art is a necessary obsession for me; I pretty much eat, breathe, and make myself live for art. Not sure if you consider it a healthy thing, either; I'm practically a hermit. A happy hermit, but still.