Write songs all the time. It can take a long time to develop your voice and craft as a songwriter. Keep a notebook or mini-recorder around so that you can constantly be recording your great song ideas.
Learn to play a musical instrument. This will help you to develop basic musical accompaniments, making it easier for you to write songs on your own. Most pop music songs are composed on pianos or guitars, as they can allow you to create rich harmonic progressions behind your vocals.
Find a group of like-minded musicians with whom you can collaborate. Form a band or a musical collective so that you can flesh out your different song ideas.
Book concerts at local venues. Bars, clubs, hotels and coffee shops can be great places to test your songs and gauge audience reactions. Live performances are probably the single best way to expose your music to the world and develop a fan base.
Enter songwriting contests to receive critical acclaim for your songs. There are songwriting contests for finished musical compositions or just for song lyrics. In addition to the attention you can receive from record executives and other industry professionals, many songwriting contests also offer cash prizes.
Send your demo recordings or song lyrics to publishing companies or record executives. MusicMoz can help you get in touch with publishers, while Singer/Songwriter keeps a list of many record company contacts (see Resources below). Be aware that many, many up-and-coming songwriters send their materials to executives, so the competition will be fierce.
Consider finding a day job with an advertising agency, musical theater or school music program to pay the bills. Odds are, you'll have to work a day job for several years while wait for your big break, so you should find a day job that will allow you to work with music, which may actually enhance your career. That way, you'll always be developing your songwriting craft.
Copyright your finished demo recordings before sending them out for others to hear. While copyright ownership is implied the moment you compose a song, it's a good to provide yourself extra legal protection. Visit the United States Copyright Office website to learn the steps in the copyright process (see Resources below).