Music is very much a random process. I might be waking up or walking and a new song just comes to me. So always have a phone with a sound recorder with you so you can hum the song. I must have hundreds of bits of music stored, some might join 3 or 4 songs together and become one. Often the music, after I have eventually gone through the process of working it out, writing the chords down etc, will still hang around for a long time. Maybe it might be a year before the lyrics suddenly come or a poem ends the process. So music is a long process for me.
Again my advice would be never to sit around around trying to write because the best music rarely happens that way, it comes to me when I least expect it. Music is a wonderful spiritual process and if you are lucky enough to have new music come to you, you should count yourself very blessed. (it only happens to the few)
In reality only half a dozen reasonable songs, those that I would consider playing to anyone-else, will come to me in a year. For me in this process there is a lot of mediocre songs, I am very tough on myself.