Art is a luxury, it rarely sells itself, it requires some effort on your part.
When you establish a connection between your customer and you/your art, your chances of making a sale go way up. You don't have to give them the hard sell, that usually puts people off, but a little friendly conversation can get the ball rolling in getting your customer to ask you about how you make your art.
Make small talk - "How did you hear about the show?", or "Aren't we having great weather!", etc. But give them a minute to browse your booth and soak in what they see before saying anything, especially if they are studying a particular piece. And, unless they are acting really interested, don't ask them if they would like to hear about your art, or launch into an unsolicited, detailed explanation of your work, that can be annoying. Let them ask you first. And better yet, try to get them to tell you a little about themselves.