I do all my songs in my mind first.

Sometimes I hear a chord progression in my head. I type the chords into BIAB. Then I try to find the style that I'm hearing too. (most difficult part is finding the style) After having BIAB play it a few times... a melody comes and I record it.

Other times I hear a melody. As I listen to the melody play in my mind, I envision changes behind it. Once I get the chords typed in, I'm ready to record.