when i was working in a factory, i'd have shifts (usually night shift) where all i'd have to do is put stuff in and take stuff out. so i'd have a lot of free time on my hands. so i started setting myself "projects" where i'd make a list of maybe 20 titles then try to write songs around them. this was after i first joined chordie so most never even made posting, but they did make a CD or two. writing this way made it's own difficulties, as i was writing words down, i usually have a tune in mind which the words would follow rhythmically. by the time i'd pick up the song (sometimes a week later) the melody would have escaped my mind completely, therefor making me find a new one. when i found one, the words might no longer fit, so re-writing would ensue, which made it more difficult as i like to write stories, so the new text would have to have relevance to the theme i already had.
i have many other ways of writing too, a chord sequence first or a riff. i have even woken-up with an almost complete song in my head. but i find the thing that changes a song mostly is the recording of it, especially if your doing a multi-track recording as i do.