Backstage Passes: The Best Way To See the Show
First off, you could join the local media as a freelance photographer or reporter. Give a cold call to the media outlet and pitch them an offer to interview and photograph the band. They're used to these calls, so if you sound like you know what you are doing, there's a good chance they'll take you up on your offer. Although, of course, this does mean that you'll have to actually do the interview and write up a decent piece.
You could also call the venue and ask if they need extra stage hands. Though the most coveted positions are generally filled by people who regularly act as stage crew, extra help setting up and breaking down is always welcome, and there's a good chance that they'll bring you on. Obviously, the potential downside of taking this route backstage is that you may get assigned a job that keeps you outside picking up trash while the show is going on, but the odds of your having a chance to make friends with one of the "in crowd" are pretty high as well. Who knows? If you play your cards right, you might just end up invited to the after-show party!
Alternatively, you could always just show up during the sound check and see if your idols just happen to be hanging around. While this may seem ballsy, it happens. I've had some great conversations with stars during their downtime before the show.
Of course, there's a number of other tricks you could employ to get yourself that coveted backstage pass, but just remember that whatever you decide to do to get in, no one likes a jerk. Play it cool and enjoy the show!