for me, its like a reciprocating relationship between lyrics and music.... once I have an idea (where it all begins for me) I think of anything, music or lyrics, and then add the other one in...... after it begins its like a battle where the lyrics change the music and then the music goes off and give new ideas for melody and lyrics............... very very very rarely will a song, at least for me, ever come all at once.... it takes many rewrites and changes for a great song to come out for me......