Fanny Gott is a professional dog trainer in Norway. On her blog, Fanny's Clicker Blog, she lists five ways to improve training sessions. The first one, playing crate games, was completely new to me, but looked interesting.
However, I was particularly struck by the idea that I should be alternating fun tug games with food as rewards for good behaviours. Lately I've only been using food. There's a lovely video clip of a training session in which the dog is obviously having lots of fun.
The session was a little hard to concentrate on, though, because the location was so stunningly beautiful!