In the opening scene also shows a poor, blue collar neighborhood and is infused with jazz and blues piano notes that consistently put the audience in the mood of a New Orleans 1940's urban poor town. That descriptive technique is what sets out the atmosphere.
When Blanche appears,she says the memorable words:
I rode a streetcar named Desire, then transferred to a streetcar named Cemeteries, which brought me to a street named Elysian Fields
That entire phrase is the complete foreshadowing of what her life is and will become: She lived for lust, and found the death of her persona, and ended up in an Asylum.
Yet, there is more: She is impeccably wearing white clothes *blanche=white (in French) and symbolizes the fake purity and clarity she pretends to illustrate* and her presence is a massive contrast against the background, foreshadowing that there will be a clash of characters, histories, stories, and personalities. That would be a second technique.
The fact that Blanche is dressed in white against a dirty background also foreshadows in the audience that inevitably those clothes are very prone to become dirty and stained in that environment and that is another foreshadowing of what will go on.
What this indicates is that Williams is already alerting the audience that the characters are indeed all extremely different one from another, and while some may be co-dependent, each has unique and independent perspective in the story line, and each has a unique set of psychologies to be analyzed.