A friend of mine was in your exact spot last year. She raised rates for new clients right away, just like loganthompson said, and kept her current ones at the old price for six months. She sent a polite note explaining the change to her regulars later on, giving them plenty of warning. Only two people left, and the extra income from new clients let her work less while earning the same. It really proved her value and made room for better projects. She always says that slow, clear change is better than a sudden shock.