Art Direction can be difficult to demonstrate what you actually do.
Here is an example of how I give notes and communicate visually with fellow artists.
The Spider-Man 2 Key art was one of the most high profile pieces I have ever worked on with many parties interested and invested in it's success.
The majority of the credit must go to Insomniac, but this is the type of notes we give at Marvel to help even the best studios push a little further and result in the best product possible.