http://mirificampress.com/permalink/pay_me_please
“Going it alone as a web designer will quickly lead to the discovery that your accounting skills are as important as your design skills. If you’ve ever done any freelancing you know exactly what I mean. When should I bill? How much should I charge? What kind of pricing structure should I use? These are questions I’ve wrestled with more than once over my eight year tenure as a freelance web designer. Fortunately, out of the heap of triumphs and failures, a refined set of principles has emerged. I’m sure these rules will keep you out of some sticky situations.”
GTFDesign 