There has to be a leader calling the shots, and you're only going to be as good as this person--it shouldn't be a vocalist, because they, just like the soloists, are waiting for a cue to do their thing--it should be someone who is playing all the time--

Soloists should have about two measures warning--and you should keep in mind that it hard to go from pounding out rhythm guitar to squeezing out a lead, especially if the bottom falls out of the music because you stopped playing rhythm!!!