You might say that the best preparation for an ERC interview is a first try. Learning to sell your research is best done by a proper preparation and then just doing it. However, you ideally have the experience before your first interview.
Luckily the needed skills and mindset can also be practiced during lectures, presentations on conferences, and media interviews. Also social interactions with non-professionals offer ample opportunities to practice your skills. If you learn to convince people of the value of your research in the pub, on the school yard, on social media, and on a birthday party, you will also be better equipped to convince panel members. In the end, just like your friends, your parents, your siblings, the parents of your child’s classmates, panel members are just human beings.
Ultimately this is not only about convincing others. Learning how to deal with your own challenges also contributes to your personal growth. As we have witnessed over and over again.