Pick the right stations. Most commercial radio stations play a particular genre of music—modern rock, country, pop, whatever—and only that genre. Not only is it a waste of time to send your country track to a rock station, it could also hurt your chances with the local country station. The stations may well share an office, a staff, even a program director.
Know who can help you at the station and who can't. Disc jockeys at commercial radio stations almost never choose the music they play. The person who decides what gets played and what makes it into the rotation is the program director, or PD. If anyone besides the PD tells you that your song is going to get on the air, don't believe it. You can contact the PD by calling the station and asking for him or her. If the PD is unavailable, leave a message, but call again.
Hire an airplay promoter, if you can afford it. Independent promoters offer unsigned acts the same kinds of services that major label marketing departments offer. It usually isn't enough just to send your song to a station; there's a lot of followup involved, such as calling to see whether the PD has heard your song, offering to set up interviews, station IDs and other appearances, and tracking when and how often your song plays.
Send the station a CD by first-class mail. This must be a "manufactured" CD, not a homemade disc burned on your computer. Recordable CDs are cheap and unreliable; worse, commercial stations see them as a sign that you're not serious. Send a single, not an entire album, and choose a song that starts strong. If you can get the PD to listen to your song, she may give it only half a minute before she moves on to the next disc in the stack. Make sure it's a "radio edit" with no explicit lyrics, no longer than three and a half minutes.
Put the CD in a standard plastic jewel case—not a slimline plastic case and never a cardboard or paper sleeve. Make sure the band name, song title and running time are clearly identified on the outside of the case.
Know what isn't going to help you. Forget about having all your friends call a station and ask to hear your song. If the station has never heard of you—and if all it has is your CD sitting in a stack with a hundred others, then it has never heard of you—the PD is going to see right through this tactic. Don't get carried away with the number of Facebook fans or MySpace friends your band has. Social media may help you book gigs—or it may not—but it's not going to get you on the radio. And finally, don't bother emailing MP3s of your songs out of the blue. The station might not be set up to play MP3s directly, and besides, PDs don't like unsolicited attachments any more than anyone else.