How does Miller use the stage set to influence the audience's perception of the tension?
Miller doesn't just pictorally show how change oppresses the Loman household; he has Willy talk about it. Willy remarks with disgust how the whole place presently stinks and reminisces about how the flowers used to give off such a sweet fragrance in the springtime. He also mentions two large elms which used to be in the yard, and at one point he gets confused and thinks they are still there.
This "interfacing" of the past and the present shows Willy's inability to accept and cope with change; he is forever seeking refuge in "the good ole days." As his house and yard Willy is a relic, a has-been, a vestige of the past - who can no longer find his place in the modern world. Little by little, his vital space has been whittled away by an increasingly competitive market:
Miller describes the setting so that there can be no doubt that the American Dream is a major theme of the piece. His use of the apartment buildings overshadowing the Loman house is symbolic of the change that has occurred in American life since World War II. A single family home belongs to the past, when the American Dream was still alive, or at least when it was assumed to be alive. The home's decrepit state details that a new reality has come into being, one that is a community of families, but a community without a central purpose. The apartment building is not like the small town of the past, where the inhabitants knew and supported each other. The families in the apartments live separate lives, even though they share a single building. There is a sense of not belonging to anything larger than oneself, that America is now a country of extreme individualism, where it is “every man for himself.” ...Willy finds that he no longer fits but he still continues to live in his own dream, hoping for a life that is gone.
- from eNotes.com/death-of-a-salesman/essential-passages
Note: Other playwrights have also capitalized on the strong imagery of a descriptive domestic setting. Tennessee Williams uses it in both "The Glass Menagerie" and "A Streetcar Named Desire" and it is ever so symbolic in Eugene' O'Neils's "Desire Under the Elms" and J.M. Synge's "Riders to the Sea."
Let's start with the "tension." Tension implies a difference, a contrast, and a struggle. What are these elements in regard to this play. First there is Willy Loman: a little, exhausted traveling salesman at the end of his rope. He can barel make ends meet any longer, because he's older, tired, and the years of competing have gotten the best of him, sapped his strength, and driven him into dreams of a more bucolic and happier past.
Now here are the author's words about the set... look for Willy:
Before us is the Salesman’s house. We are aware of towering, angular shapes behind it, surrounding it on all sides. Only the blue light of the sky falls upon the house and forestage; the surrounding area shows an angry glow of orange. As more light appears, we see a solid vault of apartment houses around the small, fragile-seeming home. An air of the dream dings to the place, a dream rising out of reality.
Can you see him there? Can you sense the tension between him and the world that is hemming him in and between his past and his very pressing present?