Bad Attitudes Don't Sell
It can be tempting to moan and cry with your neighbor when the show is slow, however, you are the representation of your product. Even if the place looks empty, you'd be surprised who is watching. Also, a bad attitude can affect your day when you do have customers. Keep a happy upbeat attitude and have fun! It will bring in more customers and more sales. People are attracted to happy people.
Don't Envy Others
Don't compare your stuff to others and feel bad. Remember, bad attitudes don't sell! You're stuff is fantastic, that's why you brought it right? Feel free to look, get inspired, but don't think you have to match others in expertise or price, we're always learning, so learn, but don't get down!
Cash Only Equals No SaleI can't tell you how many times I've been to a craft fair and I'm still seeing cash only booths. There is just no excuse for this. A ton of people either carry no cash or very little cash on them. Your sales with drastically increase if you allow credit card purchases. It's so easy via Square or Paypal. As a user of Square, I highly recommend it for ease of use, it's point of sale options and it's low price.
Use Signage and Height to Your Advantage
Craft fairs are a hodge podge of tables with all kinds of goodies and it's easy to skim over things. If there is something you particularly want to call out, make adorable signs to put on the table to point things out, especially if things are laid down on the table and hard to see from far away. Spinning off this one, DON'T just lay every flat on the table. Use height to your advantage, hang things, build racks, place things on pedestals. You want your booth to stand out.
Scope Out the Competition
Before you pay your booth, ask the coordinators if anyone else is selling the same product you are. If there are many booths selling the same product, your sales will be low and the cost of the booth may not be worth it. You want to be unique at the fair or at least one of few people selling the same thing.