I do sincerely hope one day to be able to sell my wares at one of these large fairs, but until that time, I eagerly read information about selling at craft fairs, so I can get a good idea in my mind of good display & selling tactics.
Here are some of the things I've noticed made a good booth display over the years:
Do not overstock in plain view: there was a booth I saw that sold small products (I won't mention what kind for anonymity) but they were in small packages that could be hung. Their display probably had 200 items all hung in neat rows and columns, but it was MASSIVELY overwhelming. I thought about going to look at the booth but it was literally such overload I just didn't want too.
Lighting is really, really important. If you have anything that sparkles, be sure to bring extra lighting to show it off! I saw an herbal vinegar seller whose wares were all sorts of different colours, and they had spot lighting behind the bottles that made them all shine like jewels! Extremely appealing!!
If you have a URL, be sure to display it prominently! With the busy-ness of some of the fairs, some people may not even be able to get to your booth to grab a business card, etc. but still are interested in what you sell. If you display your URL prominently, people will be able to check it out later even if they couldn't look at your products as closely as they'd like this time around.
If you do an unusual craft (or even if you don't) photos of the process is always a great way to generate interest. Often people will become more enthusiastic about your product when they see details of how it is created.
The great people over at the Folksy Blog did a wonderful series on "Craft Fair Advice" - so head on over there to read some of their great ideas for selling at a craft fair: http://blog.folksy.com/category/seller-tips/craft-fair-advice.
If you're selling this year, best of luck! And if you're like me, have fun at all the fairs out there! :)