Your strategy for a trade show or event should never be created in a vacuum. It should always be a part of your larger marketing strategy and feed directly into your business goals. So, when planning for a trade show, make sure you're incorporating all of the channels which are a part of your normal strategy.
Just like any marketing strategy, your plan should be directly related to your goals. When deciding how to properly use social media to meet those goals, think about your funnel. Specifically you need a plan in place for reaching prospects at each stage: awareness, consideration, decision and even for current customers.
Now all you have to do is match your approach to your prospect's stage!