Thing is,I stopped thinking of one thing. A song is so many things that boiling it down to guitar parts makes it really, really boring.
So, I just let my mind meander and find the hook for whatever instrument it is. Since I've started playing some keyboard/piano, mandolin and bass (well, bass for a while), I've stopped really trying to make a song a guitar song (though guitar will always be in there).
I'm not great at my new instruments but knowing enough musically has help me adapt with writing. I want to hear a sound so I figure how to make it.
So.....I just gave up and being one thing and let me mind roma free in search of an interesting sound and I think it has worked alright.