I am a professional songwriter in Nashville, TN. AMA!
I have been writing songs for the past 30 years. I moved to Nashville in 2002 and started honing my craft. Some of the best songwriters in the world are in Nashville, and not only in Country music. I have been writing for an artist development company for the past 4 years where they bring artists to me to help them write a commercial song. I haven't had any major hits yet, other than having a song on a TV show (Cedar Cove - Season 1, Episode 2) at the very end is a song called "I Could Get Used to This" sung by my cowriter Treva Blomquist. I have had songs on hold with Montgomery Gentry, Craig Morgan, and Garth Brooks, but the songs never made it to the album. You can listen to some of my songs here:
http://www.reverbnation.com/scottsanford
I know a lot about the ins and outs of songwriting from crafting the song all the way to getting it published and eventually recorded. I'll be happy to answer any questions you have! AMA!
EDIT: The one thing I didn't mention was the extreme importance of moving to a major music hub like Nashville, LA, or New York. I recommend Nashville because it's geared towards songwriters more than the others I think. So if you are serious about becoming a professional songwriter, it is imperative that you live in a major music hub. You have to be close to the business side of it. If you think you can write stuff in Boise Idaho, put it on a CD, send it in to a publishing company in Nashville, and expect them to call you up offering you a deal, you're gonna have a bad time. You know what the insiders call those submissions? "Nashville Coasters". That's all they are used for. They rarely, if ever, get listened to. You need to be able to take your cd in there in person. Get to know the receptionist. And most of all, you need to be able to come in on a moment's notice if they do call you. Think of it as a business and not just a hobby.