i think the toughest things for organizers to communicate to participates are the parameters of the protest.
for instance, here in philly there was a political rally that was held near city hall. it drew a lot of people, particluarly young people, who wanted to "march." unfortunately, the organizers only applied for the rally space and got the appropriate permits and city secutiry (police) for that sort of protest/rally activity.
When the younger ones started to march, they began to block streets, and when they started to be arrested for disorderly conduct, they bagan to sit and lay in the streets claiming their right to assembly.
well, no one was challenging their right to assembly, but the city wasn't prepared for a march. When a march is planned and permitted, some streets are blocked off to traffic so that the marchers are safe and the traffic runs smoothly in alternative patterns. THe police also protect the marchers by maintaining traffic flow and following the march so that no one gets unruly (ie, looting), or hurt.
So, the organizers kept trying to tell the kids not to march because the rally wasn't permitted to march and that it would cause a problem to the city, in turn causing a problem for the organizers and the cause. Problem was, the event was huge (probably 500-800 people), and without being able to get this information out early on, everything went ka-blooey and people had to head for the hills or else get arrested for only a small percentage (about 200 or so) acting ignorantly.
So, be sure, when you start your rally/protest, that you're clear on what you're going to do and what you're not going to do. Tell the participants WHY you've set it up the way you have.
When our quaker meeting set up a peace rally with other local churches and communities, i made an announcement as people started to gather about the legal elements of the rally--the permits that we had and what they meant as opposed to others that we didn't have and what that meant, the decorum that we should hold in respect to the township, the police, and passers-by, and any other sort of "logistical" elements that needed to be conveyed.
It's important that that information is out there so that future events will run smoothly, without unnecessary arrests and what not.