good point from PackageID. Smaller jobs for clients i havent worked with before are asked for 100% upfront and bigger stuff i wont take less than 50%, with full paymet upon completion or at specific dates to keep the cashflow sweet.
Social networking sites are a great way to find work, offer your services to bands, Djs and promoters if flyers are your thing, but be cautious of the payment situation.
http://www.freelanceswitch.com is a great resource with a huge archive, dig around Noisy Decent Graphics , this guy really does speak some sense…