Once I recognized that I was doing this, I tried to
If you feel yourself starting to drift back to your work. Look back to your customer and ask them a question to get the conversation going.
If it looks like your customer is about to walk away, continue your demo by pointing out the next thing you are about to do. Then start doing it with a running commentary. Explain how the technique you are demonstrating relates to the finished pieces you have for sale.
Most important: always remember that your ultimate goal for being at an art show is to sell art, not to teach art.