A short YouTube video on basic skills in how to facilitate a focus group, showing one poor one and how to do it better is here: https://www.youtube.com/watch?v=Auf9pkuCc8k

A longer video, in which Richard Krueger (leading author on focus groups) demonstrates some strategies for how to manage interaction within groups: https://www.youtube.com/watch?v=xjHZsEcSqwo