Q: Give me a tool to put in my songwriting tool kit please.
A: timed run throughs, with a metronome, and walk over and touch the door handle before each one. and shut the metronome off just before you get to the split point (the end of what you are sure of so far) and sit silently and try to catch the lightning bolt. it will be at its clearest within 1 second of reaching the split point. then brainstorm all the traces of things you might have learned. play 'what do we know'. then do another run through. putting ear plugs in and jogging in place while doing the run thru in your head can also be a good way to find the answers