Several posters mention using good graphics - this is really important. People wandering the aisles of a trade show are not going to stop and read all the words some clients want to put on their displays and banner stands!
Instead, put up a great image that catches their eye and arouses their curiousity.
And have a plan for screening visitors to catch the potential customers.
and have someone in the booth that knows the product and is good at chatting with people.
and...and..bottom line, there is a lot more to having a successful trade show than just showing up, sitting down and reading the newspaper