Be prepared for change. It is unlikely the designer will suddenly suggest a change, but external influences such as manufacturing considerations, production costs, electronics development, marketing decisions and competitor activity can all force a change in detail, direction, or even a total rethink.
Stay informed. You will be a key decision maker what can be a complex process. The designer should try to make this as easy as possible for you, and keep you informed of what is happening throughout a project. Try to take time to read messages, respond quickly when information is needed, and generally keep abreast the process.