More cases than not, a project will have requirements that will not always be complete.  At times, clients seem to think that they can provide you with a set of requirements, come back in six to eight months, and get a quality system. Because of this, it is difficult to make your client understand that they are vital to the success of the project.  In my personal experience, the way to cross this bridge is through communication.  Here are some examples of practices you can put into effect on your project to increase client-contractor interaction:

Release Planning: Instead of just analyzing the requirements and planning releases based on them, determine the total number of development hours available for the given release. Then, under your advisement, let your client them pick and choose what they would like implemented in a given release.

Weekly Elaboration Meetings: At least once a week, schedule some time where your client can come to the development site and interact with the developers of the project.  This way if any of your developers have any questions about requirements, the can get the necessary elaborations to get the job done.  This will make your client feel like they are truly needed to make this project a success.  And will often open the lines of communication for other times outside of this weekly meeting.

Real-time Development Sessions: Get your client in a room with a ‘clickable’ design.  During this session, solicit their feedback and try to incorporate some of the small changes on the fly.  Using an approach such as this can be utilized to provoke thoughts and ideas from your clients. If these sessions are managed effectively, it is a great way to get you and your client thinking as one team.  Having the luxury of knowing your clients expectations will let you develop customized management strategies that tailor to your client.

Extended Testing: A week or so before a release give the application to your clients and let them play with it. Have somebody from your team in the room to document their findings.  Take back the findings, perform some analysis and determine what you can fix for the release.  This goes a long way with a client in establishing a client-contractor trust which is otherwise difficult to come by.