I've had songs just come to me on occasion that were pretty complete the way they were, and other times I can work on a song for over a year and although I like the idea of the song when I start on it, I can't seem to make it to the finish line. The songs that just come to me, cause me to wonder if I didn't accidentally tune in to some sort of cosmic energy source for song writing. Does any one know of a method to sort of channel such an energy source, if in deed one actually might exist?
Suggest you checking out Nahre Sol's youtube channel. She gives tons of ideas (and techniques) that help you formalize a particular musical idea. She had an hour long discussion on how to end a song. One such composition technique that i found useful was to isolate a looping musical idea (e.g., a repetitive section) and then building other voices on top of it.
The answer is simply "write more songs." If you write 10 songs a week, you will produce 10 times as many "good songs" than if you only write one.
By all means put something on one side if you can't figure out "what is wrong with it," and come back to it later, but spending a year trying to make one idea "work" is probably not the best way to make progress.
Does any one know of a method to sort of channel such an energy source, if in deed one actually might exist?
There are plenty of books, videos on YouTube and other sources both online and not which are dedicated to this topic. It's hard to answer so generically, hence the so broad recommendation: I suggest you research on your own based on where you are (composingly speaking), what genres you're interested in, etc.
Some time ago I read some Pat Pattison's book and made a Songwriting course with him on Coursera. He worked with great people and is very clear when transmitting his ideas.
Hope this helps!