I have done some freelance writing, but not enough to call it a job by any means. I just write in my area of of interest and submit to like publications. I've had good luck so far. I follow the basics of writing from college English 101 or whatever that was, and so far so good. I have submitted 6 articles and they have all been published.
There are online sources, local newspapers, magazines, tech writing...there are a lot of opportunities out there!