Create a party set up (food table, dance floor, seating area), put some music on and invite your children to enter the party as their character/book. Or provide stickers for the children to wear.
Where would they go? Who would they talk to? Who might they try and avoid?
Support the children with introductions and ask them questions. Stop the music to freeze the party and ask them what they are doing and why. Children who have opted for a non-fiction title might need additional prompting – encourage them to consider the fictional characters that would most like or need their book.