I started this by picking up the guitar after having put it down for a number of years. My goal was to learn how to write my own music, so I started an object writing group. I pick a word of the day and write free association for about ten minutes starting with that one word.
Seeing some of what came out of those writing sessions, my guitar teacher encouraged me to start writing lyrics so that's what I did. Now the lyrics come easier than the music. I don't have the 'feel' of music like I did in my youth. The words come easier. And when I revise them, reorganize them, put them to a meter, rhyme structure, tell the story, and keep rereading it, melodies start to emerge. I can sing those to my instructor and he can pick out the chord progressions. We've not gotten farther than that up to now, but I hope to take this all the way and finish some songs.
There's one song I hear in my head down to the vocal harmonies, thundering drum rolls, and flute flourishes, but I have no way of making it real.