One of the often-overlooked rules of reinforcement is to use a variety of reinforcers. The two key words in that sentence are variety and reinforcers.
We're all creatures of habit, so it’s easy to fall into a routine where the reinforcement is well...routine. I like sushi and reward myself with it at lunch, but offer it to me on the same day for dinner and I don't find that reinforcing at all!
So a key to successful training is to keep it interesting. Vary your reinforcers. You can mix up reinforcers in the same session. You can vary them from session to session.