Write your songs down. You will want to be able to present your songs in a professional manner before you shop them around to music producers. Your music sheets can be handwritten, but using notation software such as Finale is a better idea. This allows you to write and print professional-looking sheets for your songs. It also gives you a hard copy to file when you register for a copyright.
Record a demo of your songs. Today, with the availability of digital home recording equipment and software like Pro Tools, it's easier and less expensive than ever for a songwriter to produce quality recordings. Along with printed sheet music, you'll want to submit the best recording possible. Be sure to have a full band perform your songs when possible. The closer to the actual song you can get, the better a producer will be able to determine the value and quality of your songwriting.
Register your songs with the United States Copyright Office (see resources). Although your songs are legally copyrighted the moment you create them, registering with the U.S. Copyright Office adds an extra layer of protection for you, should you ever have to file an infringement suit. The registration will be concrete proof of authorship and the date you claimed authorship. There is a small fee associated with registration, but if you're sending your songs out, it's better to be safe than sorry. You can register and deposit a copy of your work by filling out an online form.
Purchase a copy of the "Songwriter's Market," which is published by F&W Publications. It's the one resource every songwriter should have. The book lists hundreds of music producers that purchase songs. Listings include complete and accurate contact information, how to submit your song, where to submit it and to whom to address your submissions. The information also tells you how much you will be paid for your songs. This guide is a must-have for anyone serious about selling songs.