Good questions!!
To take East as an example. A bare stage apart from some chairs against the back wall. When the actors are not performing they sit on the chairs. Sometimes a simple table is brought onstage. Mostly the actors perform on the bare stage.
Berkoff as a director know the importance of lighting. No gimmicks but the lighting will help focus the audience on certain characters.
The actors use mime a lot- the fight scenes in East should be deliberately "staged" as if a dance, so symbolic violence. In the eating scenes there are no plates or food, but the actors mime this, and typically very fast, as if they are stuffing themselves.
The mine is often one of the highlights of a performance, such as the motorbike scene in East.
There are photos of productions here
www.iainfisher.com/berkoff/berkoff-photo-all.htmlEast, Greek and Kvetch give a good feeling of Berkoff's vision.
Does this help?
Iain