Don't always simply give the reward -- sometimes make the chase for it. This means that when you're opening your hand to give them food during a break, step back a bit and have them chase it instead of just shoving it in their mouth.
"Variable Rewards" is what makes games like slot machines addictive. Sometimes you win something, sometimes you don't. You can be the slot machine for the dog. In practical terms, change up the frequency at which you reward your dog with the food, toy, or praise. For example, instead of rewarding the dog after each command, maybe you do 2-3 commands in a row before you actually give them a BREAK and REWARD.
And when they learn something new for the first time, give them multiple awards in a row (these are called Jackpot Rewards!).
Ending the game at the peak of their interest makes your dog anticipate and look forward to your next training session.
Spice things up by starting a training game at a random moment, like when your dog looks at you. For example, if your dog is looking at you as if he or she is responding to a FOCUS command, give them a BREAK and REWARD and kick-off a training session.
