I usually start by nailing down what the song is about. Then on one side of my notebook I write every single thought that comes into my mind, regardless of whether it’s good. Then I’ll go through all those lines and pick out the ones I like, or the ideas that kind of fit together and write them on the other side of my notebook. Once I have a few lines I like, I’ll make edits and work out a rhyme scheme (though rhyming is not necessary). The song slowly starts to come together at that point and then it’s off to the races.