Consultants : how to advertise oneself and still remain discreet

The job of a consultant, which is based on discretion, expertise and the ability to listen, does not seem to be affected by marketing concerns. However, competition between the different consultancies is making the sector increase its investments in communications. Whether it is mass publicity campaigns, or confidential discussions with the client, the range of strategies and operational methods of the consultant is vast. What should one choose to advertise when one is a consultant ? How does one commend oneself without revealing one’s practices or damaging the client’s interests ?