Your products should vary in price from a few dollars to more expensive items. They will help sell the more expensive ones. It's best to have a helper as it may be hectic at times. Also, there will always be someone there when one of you needs to leave for some reason. Create a professional image by being well groomed and appropriately dressed.
Many sellers wear special costumes in keeping with their total display or line of goods.
Have business cards and brochures to promote your business. Even if you hate to sell, remember that is what you're there for. Salesmanship involves looking people squarely in the eye, smiling at them, talking to them. Above all, don't sit around reading a book or looking bored. People who demonstrate at a fair usually outsell those who don't.