Schedule the meeting when all department heads can be there, and encourage assistants to attend as well. Keep focused. Don’t let meals or cell phones interrupt or interfere. Take breaks if attention starts to lag. Protect against side conversations. Notice who leaves the room and make sure someone is taking notes for them.
Allow enough time to review every scene in the script. Keep tangents to a minimum, a very tiny minimum. It is best, from a producer’s viewpoint, to proceed through the script by shooting schedule. So if Day 1 is composed of Scenes 25, 2(part), and 221 for example, those are discussed in that order. There would be certain scripts that would be better to break down at the meeting in script page order.
Be sure to identify which department is responsible for what elements. Never assume. Is the rain the responsibility of Mechanical Effects, but the lightning the territory of the Lighting Department? Who coordinates between departments to make it all work together? You might have 15 or 20 departments involved. Don't let anything fall between the cracks.
Find the holes. The director, producers and ADs should have broken down the script completely. Each breakdown page for each scene must be thorough and detailed. From this comprehensive review, each of the departments must bring in their own breakdowns.
Be careful of new ideas. When changes are made–a newly scripted scene, another way of doing a scene, a piece of stunt choreography– they must be communicated to all departments. Nobody should be surprised on the shoot day. In addition, a department might be able to trump your good new idea with a better one. You want to keep all creative exchanges fresh and constructive.