For me there are two completely different ways to write. The first is sitting down with the sole purpose of writing a song. These can turn out to be good, ho-hum or totally useless, depending on the inspiration level.
The second is when you pick up your guitar and all the frustrations and all the crap you´ve had pent up inside of you just comes pouring out and the words seem to flow and the tune just appears out of nowhere. These are the killer songs - they dont have to mean anything to anyone else but, for whoever wrote them, this is what making music is REALLY all about.
J.