1) Vertical specific and regional shows return the best bang for your buck. Unless you have a gazillion dollar marketing budget avoid the big general purpose shows. Why? Because when you are focused on your shows your odds of having interested attendees go way up.
2) Bring lots of business cards. Make sure that someone looking at your card knows what your company does. And have it blank on the back side for those hastily scribbled notes.
3) If you're introducing new products bring in the entire field sales team. Not only do you energize the team, they can start talking about the new products to potential customers right away. And they'll have questions. And you're there to answer them. When they go home, they'll hit the ground running.
4) Simplify your booth. On your banners be explicit in what you do. Lose the cute slogans. Make sure other banners can be used as a selling tool. Instead of handing out glossy brochures (which get tossed in the trash), point to a banner and walk a customer through your product.
5) Embrace the Brownian motion. Don't over schedule your time. Walk around, see what other vendors are offering, talk to random strangers. Otherwise, why did you come if not to learn and connect?
6) The 48 hour rule. If you made a commitment at the show, make sure you follow through within 48 hours after the show. Interest decays rapidly with a very short half life. And you need to demonstrate commitment to build relationships. And this is an easy place to start.
7) Just because you have a show list of all attendees does not give you the right to spam their email inboxes. And if you do call someone who was at the show and you did not meet, make sure there is a single point of contact. Nothing makes a company look more foolish than three different people communicating with the same potential customer. With the CRM systems available out there for free, there is simply no excuse.