The NYTimes has a terrific interview with 5 top casting directors.
Here was the gem for me:
Q: What's the secret to a great audition?
Answer from Jim Carnahan: One of the biggest traps that actors fall into is trying to be what we want them to be, and that’s not what we’re looking for. It’s like a blind date. You’re better off just being yourself.
The whole thing is here.