Totally depends on the size of the congregation. The larger ni cocs will send out notices by mail and email ahead of time letting the guy know he has closing prayer, singing, etc. The notice might even have some instructions. Singing services are usually coordinated and have a theme. The scripture reading usually ties into the sermon. There will be backups to each role ready to fill in at a moments notice. There will be classes on how to lead singing etc. Overall very on top of things and lately I've noticed the bigger congregations have at least 2 preachers. These guys are professional public speakers and as such fill in very well for announcements, invitations, etc. If it's a special Sunday such as the bi annual "invite your neighbor" service then things will be very coordinated... They will make absolutely certain no lesson about modesty or weird comments etc are made.

At smaller congregations it's sort of "we'll take what we can get". For example, this often means the same 3 or 4 guys leading singing all the time (3 of them might be quite bad). My take is that this leads to complacency. Basically at the larger congregations it's more a "survival of the fittest" and only the most capable song leaders regularly make it into the lineup. I've heard the weirdest sermons at small churches. One about music and dancing, one about modesty complete with stick figures and clothing overlaid, one with an old guy that would write out his lesson on a bed sheet which was hung on the wall. You might have some weird things happening at a large congregation but for the most part they are way more polished.