To succeed at getting a song published, you must do three things:
Finding the right company
Many attempts at publishing fail because inappropriate material is sent to a publisher or record company. Don't send a jazz song to a company that specializes in Country and Western. As well, don't send a song you want recorded to a print publisher. This may seem obvious, but many do not take the time to do this basic research.
A good way to find out if the company you've selected is a good match for your song to look at the company's catalog. Websites, of course, are a good place to start.
Preparing and sending materials for submission
The two important keywords here are "clean" and "professional."
For print (choral, vocal solo, keyboard, handbell, other instrumental), send a neat manuscript. Most publishers expect copy created with a music typesetting program such as Finale (http://www.makemusic.com/). If you send a handwritten manuscript, take pains to make it as neat as possible. A clean and neat manuscript says that you know what you're doing. Send a recording only if you happen to have one. Most print publishers want to see a manuscript that stands on its own. If your manuscript requires a recording to be understood, then you haven't done a good job of writing it.
For recording, send a demo. Do NOT overproduce this. What's appropriate is a matter of opinion, and opinions vary widely - very widely. Keep in mind that you want to get the basic song across, not how artfully you can write horn parts. Companies want to hear your melody, not your arrangement of it.
Send a brief letter. State the song title, no more than one or two lines about the target market, and how to contact you. Close with thanks. Publishers and recording companies get hundreds of submissions weekly. They appreciate straightforward, brief communications that are professional and to the point. Do not try to impress a company with how others like your song.
Being patient and persistent
Because of the high volume of submissions, be prepared to receive an answer no earlier than eight to 12 weeks after you submit. After 12 weeks, get in touch and politely ask if your material has been reviewed. After 16 weeks ask for an answer or for your materials to be returned.
Do not call and say "I just wanted to see if you got my material," or "Can you give me an idea of what you think?" This creates a negative impression.
Do not submit to more than one publisher or recording company at a time. How would you feel if you accepted a song, began planning how to use it, and then received a call or letter from the songwriter saying that another company had accepted it? Most companies will write you off. They'll automatically return your submissions without opening them. They do not have time to waste on people who multi-submit songs.
Roughtly two to five percent of all songs submitted make the first cut. Only about five percent of those that do ever see the light of day.
Write the best song you can. Send it out. Write more while you wait to hear. Treat songwriting seriously, even if you do it as a hobby. Doing so will increase your chances of success.