I'm no poet but I love words and playing with them. Even when I first started trying to write songs as a teenager, I tended to veer away from what I would call 'standard themes'. When I was 'in lurrrrve', I just couldn't force myself to write love songs. When I got politically savvy, I couldn't write standard protest or smart observational. When I became a christian, I tried to write 'acceptable' stuff but writing to order is something I just can't do. So I just write whatever comes into my head and once I start, most of the lyric will come. A lyric about my kids or school or some aspect of a faith in God or working life or death or funerals or bitterness.......it's all valid if the music and overall sound is good. At some point I know I'll have to finish them up and maybe flesh them out or drop segments.
When I write a lyric 95% of the time there's no structure, that is, I'm not writing to an already existing tune or melody. I have loads of lyrics lying about. They're not poetic, in my mind. Some are humourous, some serious, some backward looking, some are stories, some are present day observations, some are cryptic utterances.
Similarly, I always have pieces of music lying about. I'm not a skilled player at anything really, but I can turn my hand in a rather average way to a few instruments so there's always music being created. Sometimes I have to consciously
not write. It feels like I'll never get all my snippets recorded. I like putting different segments together to make a piece and once I've put music together, or at least an outline, I'll check the assorted bits of paper I have with words written and something will always eventually fit. It's not an unusual occurrence for lyrics to be given no choice but to fit with the music !
So in the end, neither comes first. Except in very rare circumstances when music and words have actually come together (or at least snippets have), both initially find their way into this world as separate entities.