Other guys have answered 1 fairly well, so I will talk about 2.
The biggest thing is to be in a good state of mind. Here are a few things I'd focus on:
1. Get a solid night of sleep before. 8-10 hours. Make sure no electronics and be in a dim space 2 hours the night before.
2. Have a nutritious breakfast the next morning. Do some brainteasers and then just go for a walk or a run. Then put on your suit and tie.
3. Right before the interview, do a breathing technique. In 4 seconds, hold 4 seconds, and out 4 seconds. It'll physically calm you down. Also, force your face into a smile, and hold it for a minute. That automatically improves your mood and will remind you to smile more during the interview.
Those are my bags of tricks. Good luck!