When I was auditioning for Music Conservatoires, I was worrying for a long time beforehand about how nervous I'd get. The difficulty is is that you never quite know how your nerves will go until you actually do the audition itself! And then you have to deal with them there and then so they affect your performance as little as possible.
It was then that I read the book, The Inner Game of Music by Barry Green. I found it tremendously helpful and still refer to it today. It is not too long or wordy, and is a very useful read. I recommend it to everyone!