Is it more typical for the tune to be composed first and the words fit to it or the reverse?
Who composes the beat & the musical interludes (by which I mean the music that is played between the sets of vocals)? Are these by the guy who writes the tune? The “arranger”? The individual musicians? I am guessing the arranger does at least one of these, because otherwise I can’t imagine what he/she does altogether, but you never know.
I would imagine this might vary by song, because there are some songs in which the musical solos are an integral part of the song (e.g. Devil Went Down to Georgia) and others where they’re less so.
It’s different for each songwriter and for each song. I wouldn’t expect the solos necessarily to be a factor, either.
Usually, the songwriter(s) contribute the tune and lyrics, while the rest of the band deals with their own parts in rehearsal.
I don’t know what’s typical, but I always assumed the lyrics always came first, then music was thought up to fit the lyrics. I remember being gobsmacked when I found out that HTR always writes her music first, then has to figure out what the song’s about and come up with lyrics to fit the song, which sometimes makes for some odd but interesting phrasings. The only time we’ve been privy to the process was when she recorded a trance instrumental for a compilation album, then later decided to put lyrics to it for a different recording. She arranges all her own music too.
When I was in a band, we generally wrote the music first, and then wrote lyrics to fit. In fact, we usually started with the just backing instrumental parts and the general structure. The melody and lyrics almost always came last, and were usually written concurrently. I suspect most bands that write together as a group do it this way, while singer-songwriters, as well as bands whose songwriting is done primarily by one member, are more likely to start with the melody and lyrics (and basic chord structure), before working on the arrangement.
I’m certain it varies, writer to writer.
Rush, for example, is famous for having the lyrics and the music written in entirely different venues. The lyricist is somewhere, coming up with lyrics, and the other two are writing music that they think is cool. Once they’ve got enough of both the swap and try to find music to fit the lyrics (or the other way around) counting on it working out in the end.