During my undergrad, I was a co-director of the movie club on campus, and we were lucky enough to get free advanced screenings 3-4x/month. I would be the person checking tickets, reserving seats, and managing any issues. I thought it would be useful to explain how a free advanced screening usually works and how to make it a pleasant experience for both you and the organizer:
1. Come early-many screenings will distribute 1000s of tickets to get 300 people to fill a theater. The time to show up will dependent on your location, but assume 1-1.5 hours as a safe guideline. In Philly, this will get you an average seat, NY, a wonderful seat, and NYC, probably one of the last seats!
2. Try to get your group to all arrive at the same time-If it's a really big movie (think Social Network, Thor), you probably won't be able to save seats in line or in the theater. It's a huge headache for the organizer who is trying to get *every* seat filled...and it's not fair to those who have been waiting in line.
3. Don't go for reserved seats. Before attending screenings, I would have thought this was obvious...yet, nearly every screening I hosted or attended has had some kind of issue with reserved seats. Reserved seats are usually for the people running the screenings and their guests-telling *them* that you have been there before them won't work...and will probably get you a much worse seat than if you had picked a non-reserved one to start with.
4. Be nice to the organizers. If you seem to be on the verge of making it to the movie (as in, you see a huge line of ahead of you, but you were there relatively early), make sure to keep your cool. As an organizer myself, I had little to no incentive to get seats for the people screaming at me about their seats! On the other hand, I was able to get pairs of people to sit next to each other by consolidating groups and asking if their friends had really "gone to the bathroom" or hadn't arrived yet.
5. Be aware of the line. I've been to some ..less-organized screenings and sometimes it isn't 100% clear where the line should be. Keep your head up when it's 20-40 minutes before the movie so you aren't left behind during a mad rush to the show.
Of course, follow any and all directions to turn off cellphones, get bags checked, etc, and enjoy the show!