I would like to set out a challenge for all consultants regardless of your particular area of expertise. Whenever you are asked to help a client on some problem, I challenge you to leave the client more equipped and more confident to deal with the next similar issue that arises. For example, you are asked to develop a system to deliver a particular function. You really are hired to simply develop that system. However you can deliver more than the client expects if you can help the organization deal with similar challenges in a different way. Many times the system can be used to solve similar issues. By helping your client understand the way to deal with similar issues, you become a hero and the client will be happy.
If, for example, you are ask to help develop a plan, a real value for the client would be if it became their plan not yours. Often by working with the client people, the plan will be owned by the client and the probability of the plan being successfully implemented becomes very high. Of course this will involve having the client participate in the planning and making the key decisions.
Another example is working with key client people to increase their confidence. Sharing your knowledge and your thinking with client people may not be part of the assignment but will enhance the organization ability to make changes. The value of such service will make to invaluable and increase the likelihood of a continuing relationship.
The real key to the success of this approach is your vision of your role as a consultant. Can you be more than a technician who fixes a problem? Can you be a good consultant with technical skills who makes things better?