Enter all contests and promotions that give away access passes to events. Go all out by being as silly and uninhibited as possible, within the bounds of decency and the law, if this will give you a creative edge against the competition.
Check online auctions and newspaper ads for people selling backstage passes they won themselves or obtained through personal or business connections. Start looking a week or so before the event. Place an advertisement letting others know you are seeking backstage passes as well.
Get to the venue early. Walk around to where the tour bus is located. Make friends with the roadies and others working the show. MTV News recommends that you offer to help lift heavy equipment or be of service in some other way. You might get lucky and be invited to join the elite few offered backstage access.
Form a fan club with yourself as president. This is often helpful if there is a particular performer or band you are eager to meet in person. Organize your club as far in advance of a concert as possible. Contact the promoter once the concert is announced for your area and tell him who you are and that you would like backstage access. Be persistent, and your hard work could pay off.
Apply for a job or internship at a local radio station or newspaper as an entertainment reporter or assistant. Express interest in covering all the concerts that come to town. Ask for press credentials, which can often be the ticket to meeting performers in person. This may not help if a concert you are interested in is scheduled for next week, but it could set a foundation of future access for you.
Another longer-range plan is to consider getting a job with the venue where tickets are sold. Backstage passes are sometimes available for sale, and you would be privy to this information in advance.