Keep up with current events, people and issues. Read the music section of your local paper. You'll pick up what clubs, labels, and bands are hot in your area of interest. Your favorite record store should have a selection of magazines and papers. Other people at the show will have similar interest and goals as yourself.
People love to talk about themselves and their work.
Expressing a common interest will create a bond. Don't always try and meet the head of the company. You're most likely to strike a friendship and relationship with a peer who works in the company, and will call when they hear of an opportunity. Most conventions have volunteer programs that allow you to work in exchange for a free registration. Many people working in the industry will be volunteering alongside of you, giving you an extra networking advantage.