It would be very easy for me to say that PhD candidates shouldn’t worry about being nervous. After all, I’ve finished my PhD, and any negative things I remember about the experience are in the past. I’ve also got several years of experience of talking to candidates and graduates: I can’t say “don’t worry” except in a reassuring I-know-you-won’t-believe-me way. If you are prone to nerves, there is very little I can do in a piece of writing to help you avoid nerves entirely.
But perhaps I can share some things with you that could minimise their impact. I’ll do my best.