I either start with lyrics, or wit a melody, one or the other. My songs are poems; I just have to wait until that specific state of consciousness comes to me, and I write, on pen and paper, usually I get some insight or image and then I do stream of consciousness. After that, I arrange the words and idea chunks into a coherent song form. If it's a melody, it usually comes through me, often early in the morning, between 6-9am, and I quickly record myself humming it into my phone. I then apply the appropriate chords later, and rhythm, and counter-melody/baseline. Often though, I'll put all the instrument parts together in my head/imagination, before I actually play them and figure out what the notes are. Or, I'll play around with chord formations, and a melody will emerge for me.