Find colleges or institutes for musical training. Use these courses to hone your skills and find like-minded students in said courses to connect with musically. Compose your song. Record a "first draft," rough recording using recording software and a CD burner.
Seek a copyright for your song and lyrics. Go to copyright.gov for more information. Copyrighting lyrics will usually cost about $50.
Get the song professionally recorded. Shop around for various recording studios in your area, most of which charge by the hour, yet few also charge a flat rate per song. Keep in mind that studios which charge a flat rate may not give as much attention to your recording as those which charge by the hour. Ask the studio producers if they can provide background musicians for the track.
Make sure you sit down with the studio producer and explain what kind of music you want to make sure that the producer's vision aligns with yours. While recording the track, heed the producer's advice on whatever improvements should be made. Consider recording a few songs for a complete reel to show to prospective agents or publishers.
Acquire an agent or manager to represent you. This can be very difficult, yet possible by either having an established musician recommend you, or by finding an agent that accepts unsolicited material. Join one or both the American Society of Composers, Authors and Publishers (ASCAP) or Broadcast Music Incorporated (BMI), which will makes sure you gain the royalties for whenever your song gets airplay.
Have your agent submit your reel to various publishing companies and brands. Schedule meetings with business owners and show them what you can provide as a commercial song writer. Be flexible to any changes they might make to your product.