When I step into a “scene,” I rarely know what’s going on consciously. I play my part, knowing on a subconscious level what to do.
I usually see the “scene” years ahead of time and write my part according to my feelings at the time of knowing. My feelings aren’t necessarily the same at the time of happening. This usually guides me away from the other players, because I tend to not like them very much. I only like them just enough to stay in my role that has been agreed upon.
When I’m playing my part, I’m usually saying “commands” or acting them out, by say, moving something a certain way so that the light catches it just so, or something like that.