Many people break down their scenes with coverage, as more focused filmmakers often decide to only shoot exactly what they need.
For those who have conventional film training from a video production program they may lay out a standard formula for shooting a scene. What you do is to first shoot the scene in a master shot, which is a relatively wide angle that shows almost all of the action that is taking place. All of the characters move around within the view and no person is looked at specifically. Once you do this you do the entire scene with medium shots on different spots and characters. After this you do your close ups, which requires again doing the scene correctly but with the camera focused in tight on each of the characters. This is called coverage, and though you do choose exactly how you want each shot framed and the depth you would like to show it still works in this type of pattern. After this you then cut these together, making sure to establish the scene in the beginning using the master shot. Though this is a reliable way to approach a scene, it is not always efficient and is often not going to get you what you want. Instead of filming in a way that makes you film three or four times the amount of footage that you want you can choose to film only what you know you are going to use.
Knowing What You Want
What this means is that when you approach a scene you are going to have to know exactly what type of images and focus you are aiming for. This requires very meticulous storyboarding ahead of time, or instincts that are right on the money. The reason is that this is going to make you go very quickly and you are not going to have footage to fall back on in case you do not end up getting what you want. To do this your vision for the visuals of the film must be incredibly solid.
Editing With the Camera
To do this, which is often called editing with a camera, you focus on exactly every bit you want to use. Instead of actually using normal ratios for close ups and master shots you will probably be using angles that are somewhat in the middle but unique to your specific situation. This can be pairing people together in one shot, while using tracking for the remaining crowd. Along with this is going to be incredibly short takes for each angle because you are intending to shoot only what you need. Even though you are trying to cut this as close as possible, it is not advisable to just shoot exactly what you need. Go ahead and go a little before and after with the script on each take.
This is a very classical approach and it is why many filmmakers of the forties and fifties were able to make their films so quickly. Even more contemporary filmmakers like Robert Altman and Peter Bogdanovich have been known to simply shoot what they want instead of using coverage as an approach. Woody Allen avoids coverage completely and shoots all of his scenes in master shots, instead of cutting between different focused angles. Your style as a filmmaker is what is important here and if you have a very clear idea of what you want in each scene there is no reason to waste time shooting footage that you will not use.