As of now, the work comes to me so I very rarely have to look for new contracts. Lots of repeat business and word of mouth. It helps that I do everything from hosting, designing (web, graphic, and print), social media, SEO, advertising, etc. so my customers come to me for everything Web and marketing related.
Anything I can't or don't want to do, I have contractors for... This is the area I need to be better at managing if I ever want to make the big bucks. The big money is very rarely in doing the work yourself (but I enjoy it). If I want to make more money than I am now, I need to farm everything out.
I started out by doing volunteer work for a nonprofit. Made them a website for fundraising and kept in touch with companies and coworkers I worked for in the past. I've gotten a ton of business just from my contacts. I also used Guru, like Fly said, and kept in touch with clients I got there so there was repeat business. Never said I couldn't do something, because it's all opportunity.
Peopleperhour.com is another good site. I got one of my best contractors from it.