1.) Make a Demo Tape.
2.) Set up an interview with a program director.
3.) Be persistent, but not annoying.
4.) Take any job at a radio station you can get.
5.) Don't take "no" for an answer.
Making a Demo tape is an important step. When you contact a program director, the first question they'll ask is, "Do you have am MP3, a tape or CD Sample." If you can't get into a professional studio, then record yourself on an MP3 player and submit it to a Program Director. As far as what you say on your demo. You might want to transcribe your favorite radio personality as a guide.
You can also make your sample, by getting in touch with a radio station in your area and asking them if you can get a tour of the radio station. Then once you're at the station, ask if you would be able to make a demo tape. You'd be surprised to find how many radio people are willing to help you out. Once you have your demo tape, it's time to send it to area program directors for your first chance to be on-air. Remember that each Radio Programmer is looking for specific types of voices for their radio station. So don't give up.