How does the wedding rehersal play out?

basically you need to "practice" the ceremony from start to finish so that on the big day everyone knows where they are supposed to go and when everything happens during the ceremony. whoever is doing the music (live or CD) needs to know how much music is needed and when it is during the ceremony, readers need to know what they are doing, etc. is this the first wedding your friend is doing? have you already "written out" the ceremony?