Most familiar with filming know about “Crossing the line” (also known as the “180 degree rule”). I won’t cover this in great detail but essentially when doing reverse angles and cutting between the shots if the alternate camera angle crosses “the line of sight”, the characters will flip sides which is unsettling to the viewer.
This doesn’t apply only to actors, you should also consider doorways, windows, props, etc. In most cases, it easy to know how to do this with one or two characters (such as the popular over the shoulder reverse shots). But the more people or elements introduced, the more difficult it will be (you can go slightly mad even just trying to figure out something which seems deceptively simple). Of course you can also “cross the line” with camera movements as well. If you factor filming in confined spaces (let’s just say a narrow corridor for argument’s sake!) – it can also be impossible to set the camera up where you need it to be to make everything work correctly. Pretty much all of this applied to us.
We did however use the trick of “cheating the eye line”. For example if you have one character looking at another, you can make them “appear” to be looking at each other when in actual fact they might be looking at the light on the ceiling or the door handle. The illusion still works when cut together because you are drawn to a single person’s eye-line.
Thank goodness I also storyboarded the opening stairwell scene for Emmi, I suspect it might have been an editing minefield if not (apologies for the terrible art below).
It acted as a sanity check for me and also helped everyone visualize the requirements in a way that no shot-list can convey.