Often firms spend a lot time and money wooing perfect strangers to become clients only to stop paying attention to them after the project is complete. But it is through existing clients that firms can generate more business, says Joseph Jaffe, author of Flip the Funnel: How to Use Existing Customers to Gain New Ones. Instead of following the traditional marketing funnel, flip it so that you build on existing client relationships and use those to draw new clients to you.