songwriters, I have spoken with, start with the music for inspiration. This is
not strictly necessary but it usually helps set the mood.
One of my favorite
methods is bainstorming. I play with a new guitar riff and babble nonsense into
a cheap recorder. This is constructive in two ways. First, revisiting the recording
helps me remember the feel of the guitar and melodic arrangement. Second, I can
playback and listen for spontanious lyric ideas. Those perspectives form the three
basic aspects of the song's foundation; Composition, Melody and Theme. The composition
and melody form the essential feel for the theme. As I play with the sound I search
for pockets of meaning in my babbling.
I use a similar approach if I already
have some music or lyric/theme to start with.