I have long believed that all songs essentially revolve around just one line. To my way of thinking, all the rest of the song refers back to that one telling line. Two good examples are El Greko's, "There are things he can't remember/There are things he can't forget", (from "Memory") or Jerry Rasmussen's, "All I can leave you is a handful of songs" (from "Handful of Songs"). They take you back remorselessly to what the song is all about. That line does not necessarily have to be the chorus. It can come in any part of the song.
Unless I can "hear" that line in my head, there is no song to write down. So I will go along with Sandy Paton on that one. Bob Dylan once commented that you tend to "find" songs rather than create them. Jerry started a very good thread on that subject a few months ago. I only really like songs, which sound so natural that they appear not to have been interfered with by human hand on the way! It may jsut be a coincidence, but some writers seem to find this sort of song more frequently than us lesser mortals!
There is quite a Mudcat songwriting academy here, in which you can get free workshops with the likes of Jerry, George (El Greko), the laate Rick Fielding, Jed Marum, Frank Hamilton, Harvey Andrews, Pat Cooksey and John D Loudermilk. There is some marvellous stuff in those previous songwriting threads. Check them out and good luck in your quest.