You network. You build relationships. You go to meetups and meet interesting people, swap connections, swap leads. You get strong introductions, you follow up, you build client relationships. They like you, they trust you, they want to do business with you, and they're willing to pay 4 or 5 figure sums for the privilege because you sell them more than work: you sell them peace of mind.

http://swombat.com/2011/2/24/paulina-sygulska-how-to-network... is a great article on how to network.

http://swombat.com/2011/2/25/kevin-mcdonagh-how-to-attend-a-... also proposes an approach to get leads from conferences (and despite the apparent machine-gun methodology, I'd like to qualify this article by saying that Kevin is an incredibly chilled out, laid back, friendly kind of guy).