I discovered a odd trick a few months ago, when I got stuck with one of my compositions. I had been practicing "improvising" with my eyes shut so I could visualize the chord progressions and relationships and I really got into the lovely easy flowing style. It was FUN. I didn't have to worry about form and development of themes, I could just play pretty sounds.
I was pleased until I found that this new-found freedom had somehow leaked into one of my compositions. It flowed beautifully but as one friend, an opera singer very much into music of the Romantic era, remarked ... "where is the melody?" I didn't understand immediately what he meant, until I recorded the whole thing and realized that there were a lot of pretty motifs but no distinct or memorable melody.
A few days later I found the answer. There were no "ear worms" .... those fragments of music which somehow get stuck in one's ear and repeat until you feel you're going nuts. We all remember favorite songs or fragments of the classics which we love. And we love them because they're memorable. They stick in the ear.
Now when I'm working on a piece, I know immeditely if it's a "keeper" when I find myself humming a fragment as I cook dinner or change the cat litter box. Then I know I've got it! After you get one of those precious "ear worms" ... then you can work on it, expand it and develop it. A single good "ear worm" melody can be the seed of an entire Symphony. Heck Beethoven did it with only four notes ... da da da DUM