I never really had one, I kind of just threw it out there.  But I would think that you could just introduce everyone to each other, put a little out there about what you expect from them as part of the wedding party (but don't sound demanding, of course), and maybe a timeline of when things/events should occur.  It really depends on how receptive each person is to the whole thing.  Some people will be a little stand-offish, some will be totally gung-ho about it, and some will just go with the flow (these are the best people), and of course you'll have the procrastinators and stragglers... LOL!  You can also tell them typical duties of the wedding party.