Type the name of the song into a song meaning search engine such as Song Meanings, Lyrics Interpreted or Song Meaning. Here you may find links from other fans as to quotes about the songs or other people's interpretations of a song.
Visit the artist's official or fan message boards. Post a message asking fans. Hardcore fans may have read interviews or heard an artist speaking about the song and can share the information with you. Especially around album release time artists are open about the inspiration behind songs on their albums.
Ask the lyricist. Contact the lyricist via social networking sites like Facebook, Twitter or MySpace. Comment on their page or send them a private message asking about the song.