Do you ever get into the habit of turning to a particular motif to the point where almost every time you sit down to write something, you end up playing that? How do I stop doing this?
this may be a slightly unexpected technique, but try writing a song as if it's appearing in a movie or some other type of video-story. imagine the scene, imagine the story, imagine as many things as you can about the world the song may live in. even if none of what you're imagining actually gets mentioned in the song, it still seems to power the songwriting tremendously, and opens up the possibilities you need. less like staring at a wall