Kinda echo Tim's method, get the melody nailed, then keep adding verses, often singing the same line all day til I have the phrasing right then move to the next. At some point i get to sing the whole song whilst thinking about something else then it's ready to perform. Some I give up on. Oddly if someone else's leading I think the first few run throughs are quite exciting and creative after the arrangement has been settled, less so. Having said that everything we do is work in progress we are always teaking things.