Once you’ve got your inspiration — once you know vaguely what you want to talk about — the first step is to simply write what you want to say. It’s okay to keep an ear out for good phrases and rhythms as you’re writing, but don’t force everything to sound good or to have a rhythm. Use the words that come to mind, if they fit what you want to say. But make sure to actually say what you want to say no matter how awkwardly you have to do it.
As you go, I would suggest you write in lines, rather than sentences. You may end up having to move words to different lines later, but I always find it helpful to have at least an initial structure to work with. In fact, I’d also suggest you write in stanzas, just like you would normally write in paragraphs. Whenever you move on to a new issue or part of what you want to say, start a new stanza.
As an example, here are some lyrics that I wrote for this book. They have to do with a philosophical question that I’ve been thinking a lot about lately. I just wrote them as they came to me, and will worry about sculpting them so that they are actually good later.
And what we see at our level is an illusion
We either must reduce ourselves to the particles that compose us
Or submit to being nothing but the parts of some supergroup
The danger of the other is that we’d be responsible for the group
What our parts do would be what we do, whether we agree or not
What our group does we’d be at fault for, whether we agree or not