For me it varies... Typically a songwriting session is my book of poems/lyrical ideas that is write in daily in front of me and i'm fishing couch-side with my guitar. Sometimes I'll start with a melody or music idea then end up about 50 miles away from what i started with: rewrites, chord changes, melody change. Most of the time im not too inspired to hear new melodies with out a fresh set of lyrics that speaks to me. It seems like it all comes together quickly if it's going to. Haha not too sure if i helped but that's my routine : )