Once you get past the organizational aspects, I'd say this is the part of the job that seems to be coming to me the most naturally. I've mentioned before that I don't come from an art background, so it's good that I can fall back on my imagination in this regard.
But there are other aspects of the job that require deeper thought on my part. As art director, I'm in my rights to not only choose and hire the artist, but also tell them what I'd like them to illustrate. On the surface, my first reaction is to say awesome (and I confess, it is). But just because I can do this and have a visual imagination (again, for a reader), does that mean I should tell the artists what I want them to depict every time?
In a word, no. I'm new to this. The artists have been working at their crafts for years. There's no reason for me to act like I know everything. It's very reasonable to assume the artist may have a better idea how to encapsulate the story. So the smart approach is to learn from these folks when I can. I should also mention that in the past Realms has had a reputation for allowing their illustrators a lot of artistic freedom, so I don't see much reason to change that. So to this point I've been rather hands-off. A couple of times I had a specific scene in mind in terms of art direction and I related the idea to the artist. But usually I give them the freedom to illustrate as they see fit.
Sometimes my feedback/opinions are sought after early in the process, and in these cases I'm happy to discuss the piece with the artist. Once I made a suggestion to one of the artists and he felt it was the wrong direction to take things and explained why. I listened to him and we did things his way. And when he handed in the finished piece I was really glad I did.
And that was the important thing: I listened. And I tucked away that knowledge gained for future reference. So today a different artist assigned to a piece sent me a sketch to look at. I applied some of that knowledge gained, made a suggestion, and was rewarded with "Oh, that's a brilliant idea, Douglas!"
I iz learning! :) There is still a lot left to learn, of course, but these sorts of results leave me glad that I was smart enough to listen to the artists instead of acting like a know-it-all.