There are many IT people but there are even more "non IT" people.
A lot of people out there need service so it isn't that difficult to get work.
Common strategies:
1) Word of Mouth
2) Flyers
3) Call Cards
4) Ads (web, press, radio, etc...)
5) Telemarketing
6) Email
Once you get the ball rolling on those fronts, having a good reputation helps.
That is, do good work (at your job) and for your existing freelance customers and follow up with them. They will tell their friends and so on and so on.
Elementary really.