Start by writing an original song that you are extremely confident in. Sing the song yourself or have a musician who is adept at singing or playing music perform your song. You want it to be something record executives or artists will find viable.
Cut a demo for your song in a well-made recording studio or at least ensure that it is of the highest quality. Invest a good deal of money in the demo because it will be your first impression to interested prospects. If you aren't capable of performing your songs up to your vision, then find an artist who is willing to record. Perhaps you can find a singer who is trying to establish a career, as well.
Establish a solid connection with someone in the recording industry--an agent, a producer, an artist or even a secretary would be good. Find someone who will listen to your song and give it a chance. Make sure your song is ready to be heard or viewed by others. The lyrics should meet industry standards and be free of grammatical errors and properly composed.
Contact a music publishing company through letter or email and ask whether they will grant you permission to send your song for possible publication. Remember that you are not really selling your song, but rather licensing the song to a manufacturer, artist or publishing company to be performed. You make your money through licensing the song, since selling it will relinquish your legal rights to royalties and proceeds.
Be persistent, and remember that you must record a commercially viable song that can easily be distinguished by record or publishing executives. Send your demo to multiple music publishing and record executives in order to gain the most possible exposure.