Regional or local festivals often book national acts as a headliner then fill the bill with local talent. This is a great way to get on the bill with a well known band and add it to your resume. Many times these shows pay little to nothing to opening acts, but you're the only one who will know for sure. Check local music magazines and the Internet for festival schedules in your area.
Get to know the booking or rental agents for your local venues. Although they don't always book the opening acts for the shows in their venue, they do have contact with the artists and are sometimes asked for suggestions. I've also run into opportunities where a band that is touring with a national act drops out at the last moment and leaves the venue hanging. In this instance, it's a great time to have a copy of your press kit on the venue booking agent's desk.
Approach a national artist directly. Often, the opening act for a well known band is someone that the band knows or likes. They will sometimes book themselves as a package with an opening act or suggest your band to the venue owners as a possibility for the opening slot. It's always good to have a national act as a reference. You can try to contact national acts via their record label, management, agent, producer or even tour hairdresser. Whatever path you choose, be polite, courteous and professional at all times to everyone you come into contact with. You never know when that seemingly unimportant soundman or roadie might turn out to be the little brother of the lead singer.
Research the tour schedules of bands that you would like to work with. Contact the venues they are scheduled to play and ask to submit a press kit in consideration for an opening slot. This is not an easy task, but it will work on occasion and will get your press kit to the venue owner.