Keep an open mind. Talk to reps at all the colleges in which you have any interest at all. There were a couple of schools that I had pretty much discounted and then when I went to the MBA tour last weekend I spoke with the reps and was really impressed. The opposite was true as well (schools that I was considering and when I found out more about the school, I realized that it wasn't for me).
I'm not sure if this would apply to the tour in Bangalore, but most people were in business dress at the San Francisco event. If it fits in with the culture there, err on the side of over dressing.
I agree with mirfan, come prepared with questions for the programs in which you're definitely interested. Not only will it leave a good impression, but you'll get some useful information that will help you with your decision and with your application process.
Listen in on other conversations. Some of the tables get really crowded. Don't get discouraged; walk up and listen to the questions that the other attendees are asking. There's a good chance you'll either get answers to some of your questions or you'll get answers to questions you hadn't thought of asking. Win-win situation.
If they have a one-on-one event prior to the fair, check out the schools involved and sign up. It'll give you an opportunity to speak with a rep one-on-one.