I think it's mostly a case of knowing people. Nearly all of my work is from people who already knew me before they needed the work, or knew someone who I had previously done work for.
Referrals and recommendations are worth more than anything else, and people will pay more for someone they know will do a good job. My two current side projects are for an old client of a company I used to work for and had worked with previously (they referred me), and a friend of a friend of my father. Previous work has all been via referrals from friends or clients. Once you do a job for someone, give them a stack of business cards and ask them to refer you to others. If you've looked after them, they'll be more than happy to do it. Since starting my business 3.5 years ago, I've never once had to actually look for work.
I'd strongly avoid looking for work on any website, you end up competing on price, and that's no way to make a living.