Best song starter when you're stuck

As a new or experienced songwriter, we all get stuck from time to time. It can be terribly frustrating. All sorts of self-doubts can creep in. (Maybe I'm not meant to write songs? Maybe I was only supposed to write one song? Maybe I just don't have that gift.) You want to write a song. You may even have a firm topic in mind. But the lyrics and the music just won't come. What do you do? I can't promise this will work for everyone. But it's never failed me. Not once. Actually, it's a 3-part...