Record a demo of your best three songs. Record labels receive tons of demos all the time, so limiting the number of songs on your demo will ease the minds of A&R (artists & repertoire) executives, as well as showcase only your best material.
Pinpoint a record label to which you want to send your music. You can find information like this in books like the "Songwriter's Market" series and websites like allrecordlabels.com. Find a record label that actually releases music like your own. For example, don't send your heavy metal music to a soul record label.
Develop a press kit. Have a good writer create an interesting artist biography that highlights your career in a manner that suits your image. Include press clippings and a cover letter describing why you are sending your music to the record label. Tailor your cover letter to the specific label to which you are sending your music.
Call the record label you are sending your music to and ask if it is okay to submit a press kit. This is the polite manner in which to submit your music.
Hire a manager or a lawyer to represent you, if possible. Many record labels toss out unsolicited demos from unknowns, so having legitimate representation will make it easier to get your foot in the door.
Mail your press kit, including your demo, to the record label.
Call the record label several weeks later and ask if it has received your package, unless it explicitly stated not to call.