Location (where I and the camera are positioned) is generally driven by the need for good composition but may be restrained by other factors. I shall consider composition itself elsewhere.
Limiting factors might be dictated by the environment or the requests of the company (“stand there and don’t move.”)
Often the main influence on where I am is the nature of the event. If it is a workshop or early run-through in a rehearsal room, then usually I rove freely around the space, with the potential to shoot in any direction. This luxury is also sometimes available during the dress rehearsal of a promenade production. Unless required to stay in one spot, then constant movement to change view is essential for the best shots. Once in a spot, composition again dictates vertical position — standing, kneeling, sitting or laying. It pays not to dress up for a shoot, as more often than not you end up doing a bit of impromptu floor polishing.
With a more traditional theatre layout, on a proscenium stage for example, I’m generally constrained to locations within the auditorium. Factors to consider here include ease of initial access and speed to move around, field of view, width of aisles and steepness of rake. Sometimes shots from the wings or even from upstage can work, although these are more atmospheric shots, and aren’t recommended during a dress rehearsal…
Always, always check with the actors and director or SM about where they’re happy for you to be or not to be. I tend towards a chameleon approach, blending into the background to observe quietly. As the actors become engrossed in their action, I am very quickly forgotten and can shoot freely.