I just listened to a fascinating podcast interview with Chris Shiflett, and while discussing songwriting, he made this comment:
“You just write until the good ideas come…”
Songwriting is a mysterious process, even to those who do it. There just isn’t really a quantifiable way to create anything. But the more you write, the more comfortable you become writing. You just have to face the reality that they aren’t all going to be winners, and sometimes you are going write things that just suck. But that’s OK, it’s just part of the process. It never gets easy, but that’s part of the mystery.