Brief them on the game plan.
While it is important to define a purpose, plan and scope for the creative project itself, I find it equally important to define how the roles and collaboration will work. Talk about who will be providing feedback and how much artistic freedom is warranted by certain aspects of the project. If a creative knows going into a project that there are a handful of specifications that must be carried out in a particular way, he or she will be able to address those, while spending time and energy on the open aspects that utilize his or her creative skill set.
