Of course it depends on the show, but first off read the directions and follow them exactly. Your quilt will probably be accepted based on a photograph, so get a good one. Originality seems to be very important in the big shows. For a machine quilting show, the quilting should be very good. That probably means custom quilting rather than an all-over or pantograph. And get this book by Karen McTavish - Quilting for Show -
http://www.amazon.com/Quilting-Show-.../dp/0974470635