Do you give your actors precise trajectories, e.g., to go from point A to B over the course of a number of lines, or do you feel that this is artificial?

It's all artificial, we just have to convince the audience it's not. I like to spike my actors so they can deliver the important lines from a given point in the frame. I light and shoot for that. That said, I don't move my camera much yet (was more concerned with learning lighting and sound on my last project). I tend to move my actors in frame to make up for it. So the necessity is for them to deliver some specific lines from certain points in the location. I put down spikes and lines with painter's tape for them to follow and land on.