The difference between a designer and an art director is fundamentally the same difference between a specialist and a generalist. An art director looks after the bigger picture and leaves the minute details to their designer brethren.
Keep the bird’s eye view: Don’t get too wrapped up in the details. Work like a sculptor. Start with a large mass of ideas and refine from there — but keep looking at the whole through every phase of the project. Let the specialists work out the small details, and guide them subtly when necessary to keep everything on track.