Well what I do when i write a song is first to come up with the main riffs/progressions. Then I start figuring out the melody of the vocals and the lyrics -- what I do is i start singin some pseudo-eniglish nonsense blabering over the riff/chords. It goes somethin like "wuba-daba-trliliava-salabada" kind of thing -- whatever comes in my mind. Eventualy I figure out what should be the rhytmical sense of the words and then I compose the lyrics so thet they fit this pattern. I think this is the most natural (for me) way in which a song can be composed. The music has alays been more important for me than the lyrics.