Note that the scene is set against a pretty wild poker game. Stanley is especially out of patience because he has been losing heavily. And we see Mitch immediately as a contrast to the others, especially with his concern for his sick mother.
Blanche is immediately aware of Mitch's difference. Her own sensitivity allows her to recognize it in others. This is a quality that Stanley does not possess.
Blanche intentionally moves into the light when she is undressing so as to be noticed. This is a manifestation of Blanche's desire to be the center of attention, and her use of her body to attract attention prepares us for some of her later lurid escapades.
Notice that Blanche's and Mitch's pasts curiously correspond since both have lost a loved person. This is just one of many aspects that will draw them together.
Again the light motif is here developed. Blanche asks Mitch to cover the naked light bulb. Ironically, it will be he who will later tear off the paper lantern in order to "get a better look" at Blanche.
The reader should be aware of Blanche's almost pathological need to lie. She lies to Mitch about her reason for visiting Stella and about her age. But as Blanche will later say, these are only little illusions that a woman must create.
