I find mindfulness to be an incredibly useful tool for dealing with thoughts of anxiety. When a thought pops in your head about how you're going to screw up or you're unqualified for the job or whatever, just label that thought. "This is a thought of anxiety." Don't engage with it and go down that wormhole; just label the thought. This is easier said than done, and takes practice, but as soon as you realize you're in the anxious thought spiral, label it and focus on being present again.

Dr. Jon Kabat Zinn, who is the head of the Stress Reduction Clinic at the UMass Medical School, wrote a wonderful and simple book about this called "Wherever You Go, there you are."