Paul Chitlik, professional screenwriter and author on the subject, fields a question about writing effective description in your screenplay.

The protagonist is really on three journeys: the “A” story — the plot; the “B” story — the relationship; and the “C” story — the internal journey dealing with [a] flaw. These journeys are intertwined and interdependent. Often, a plot point for the A story serves as the same point in the B or C story. In fact, the better integrated the three stories, the better the screenplay.