Peer preparation is definitely the best way to go, in my opinion. Practising in a group, or at least with one other person, is a great way to receive feedback on your responses, get used to answering interview style questions and hear other perspectives on the topic that you hadn’t considered. While practising in a group can be nerve wracking at first, I found it invaluable myself. I think it will definitely help with the blanking out part and help with timing etc too.
I don’t believe a private tutor is worth it or necessary myself when there are so many people and resources out there for free, but others may be of another opinion.