Tennessee Williams makes excellent use of symbolism in his play A Streetcar Named Desire as he employs the symbols of light and shadows, music, bathing, and the streetcar to develop his characters and forward his plot. Let's look at each of these.
Blanche never wants to stand in full light. She is always in the shadows, shielding herself with a paper lantern. Shadows appear behind her at various times in the play as well. Blanche doesn't like the light, for it shows the effects of her age. But also it symbolically reveals all that she is trying to hide, like her promiscuity and her drinking. She stays in the symbolic shadows, covering things up. Further, at one point, she speaks of a bright light in her past, namely, her love for her husband. But when he died, Blanche says, a searchlight went off, and her whole life dimmed.
Music is another prominent symbol in this play. The Varsouviana polka, for instance, symbolizes Blanche's horror over her husband's betrayal and the remorse she feels about his suicide. Blanche and her husband were dancing to the polka the last time she saw him alive. Now Blanche hears this polka in her mind, and it also symbolizes the descent of her life into madness. The song “It's Only a Paper Moon” is also symbolic of the “paper moon” of Blanche's life, the web of falsehoods she has woven around herself. That world tears and collapses as easily as a paper moon.
Blanche often bathes throughout the play, almost as if she is trying to wash off the horror of her life and her misdeeds. She is trying to cleanse her soul, perhaps, more than her body, and this act of bathing therefore symbolizes Blanche's knowledge of her impurity and her deep desire but inability to become pure.
Finally, the streetcar symbolizes the power of desire in human life. Streetcars run continuously, just as human desires are continuously in operation. Further, the passengers on a streetcar have no control over where the car goes. They can get off, but they cannot change its direction. People sometimes have no control over their desires either, except to deny them and symbolically get off the streetcar. The characters in this play, however, don't do that.