I'm basically repeating what others have already said but from my own experience;

Networking exposes you to potential Clients and helps you to maintain relationships with existing Clients. Advertising exposes you to a broad audience of potential Clients. Reputation takes years to establish but, once established, is invaluable. To maintain a customer base you need to work at all three. Once people believe you offer value they will be happy to solicit your services; over and over again potentially, as long as they feel you offer value.