"No amount of anxiety makes any difference to anything that is going to happen."
Anxiety about a concert, a job interview, or anything else is never going to help make it go any better. I always find that when my mind wanders and starts to act against my best interests that it helps for me to focus on things that I can control.
Two things that I can't control: the past and the future. Even if I know deep down that I should have prepared more for something, worrying about that now will not help anything. Even if I am being reasonable in expecting bad news in the near future, worrying about that will always distract me from taking the next positive step.
For some it is meditation, for some it is prayer, for others it is listening to their favorite music. Find whatever it is that gets you focused on the here and now and you will be amazed at how it puts you in the best possible position to succeed.