Promote their products and services. Circulate the list of the firm's top clients to all attorneys and staff. To the extent that you can reveal names, it is helpful for everyone to know the good clients, so they can pitch in on projects, respond appropriately to phone calls, etc. Set up a follow-up system to contact former clients. Make it easy for clients to contact your people.
Every firm talks about the importance of existing clients.
Excellent legal service at your convenience. For less than you'd expect.