We have a weekly practice and it's mandatory for people to attend if they're playing on Sunday.
I also give out song lists, song lyrics, chord charts and mp3/YouTube links up to a week or more in advance and expect that people listen and learn prior to rehearsal.
That's part of how I serve my team of volunteers.
I'm not Miles Davis nor Robben Ford and neither is anyone on my team, but I used to play with people at another church who would definitely hold their own against both and they all rehearsed as a band each week.
I'm not trying to knock the late Mr. Davis or his band...they did what worked for them...but preparation before the service is a necessity for us and, honestly, the Holy Spirit has our attention better if we're comfortable with what we're doing rather than all be guessing and wondering what's happening next.
Surprisingly, a lot of churches do NOT practice and the level of frustration among the musicians at those churches is no secret.