the way i see it...every person has there own style and method for writing there lyrics and music. Im a metalhead.. i usually sit there and screw around with the axe for awhile andcome up with a song, not just a riff, but a song that im satisified with, and then over the next day or so, write the lyrics that i think express how im feeling. But before i write the lyrics, i choose what subjet i want the lyrics to be on. such as demanding respect, hate, some girl, some kind of sadness, or slaughtering ur enemies.. Thats just me though..my songs tend to be just a lil violent :D
but it just depends on who and what u are interested in