Good luck.
In your head you need to forget 6 million and focus on Ken Bruce as being the only one listening. IIRC there's a preamble with the producers who will give guidance of what Ken might talk about with you, your interests and musical tastes etc. followed by a chat off air with him before going live when he may make reference to the things you've chatted about, family members, kids, pets that sort of thing.
And remember the pride is in taking part. Even to get to the live quiz is an achievement in itself.