If you're already familiar with the Six Thinking Hats then dive straight in. If not, then here's a short explanation and feel free to search online for more detailed info.
The Six Thinking Hats is a way of challenging thinking that was developed by Edward de Bono. The idea is that there are six different ways to challenge our thinking and the metaphor of hats is used to describe each one. People will usually feel more aligned to one/some than to others, but by challenging people to explore each hat you are able to get a better rounded view of the situation or topic being discussed.
Download the cards to use in your sessions. You'll find a pdf file to print off or png files to use online.