Try to focus on being "in the moment".
In other words, at every moment focus on the one thing that is happening at the time.
For instance, when you're waiting to be seen focus on how you want to present yourself (all positive) to your future boss.....
When in there talking to them focus on everything they are asking and talking about and answer accordingly.
No other thoughts but those that pertain to what is happening at the moment.
And, if you want, sip on a cup of chamomile and lavender tea or snack on some raw almonds before you go.
Either of those will help calm you and get you focused :)
(BTW: So does oats, bananas, cashews, sunflower seeds(unsalted), etc.)