First, start with YOU and the image you want to project. Second, examine your motives for buying space at an Expo. People don't always attend Expos for the purpose of purchasing items. Frequently, they take a business card or brochure and call the business months after the Expo. People who use Expos successfully say the real value is in the visibility and contacts they receive.
Expos are more about opportunities, possibilities, and visibility than instant sales.
Expos offer opportunities for personal interaction. Third, analyze the opportunities offered at each Expo. All Expos are not created equal. Analyze your budget. Include the costs of being away from your business during the time of the Expo as well as preparation time.