A part of my discomfort before my viva was due to general nervousness and lack of confidence in presenting and discussing my work. I knew my stuff but I wasn’t comfortable talking about it. I didn’t want to be in the spotlight!
A mock viva would have helped.
Talking about my research with friends would have helped.
Learning more about vivas would have helped.
If the viva spotlight seems at all scary to you then the best thing you can do is find a way to rehearse. The second best thing is to learn more of what to expect from that spotlight experience to prepare yourself.
Rehearsal is the key though: find and use opportunities to simulate the viva ahead of time.