Teach your dog to try things in order to create an opportunity to earn a reward.
When you play this game, try to relax and let your dog invent something interesting to try. You are not specifically interested in any particular behavior - what you are trying to do is encourage your dog to try something in order to get a reward.
If you find this very difficult to do, try picking a simple behavior (such as a nose touch). However, it can be very interesting to leave it completely open-ended and click anything your dog does and see what they invent on their own.
The more activities and objects you play with, the faster your dog learns how to work with you and how to try. A dog who learns to value trying hard is a joy to train and will be a keen training partner.