I definitely agree with the idea that a rhythmic activity such as walking of cycling tends to help in songwriting. The rhythm helps the phrases to flow (its a bit like when you're on a train and the sound of the train seems to translate into a word or phrase), and the fact that you can let your mind run on idle for a while can liberate some random(ish) thoughts which can lead on to others etc etc. I also find that I tend to drift off into a sort of daydream and end up with songs which are totally dislocated from my own life and aspirations, but which are like a flavour of a story of an imagined situation. All very therapeutic probably. The advantage of this is that I don't feel the need to make the song conform to any truth or completeness, it can be whatever it becomes, and if I like it I'll fiddle with it til I'm really happy with it then write it down. Its certainly not the only way to do things - but it works for me (its very cheap entertainment!). Looking back at what I've just written, I realise that its pretty similar to what Peter T recommends (aha, you were right then), in that it has a freely creative element, then a filter and fiddling around element. So, to test the theory - what other versions does everyone use?