Ehh I just did a big presentation/essay about Streetcar.
One of the big things is the social context of the play, or the 'world' of the play. Examine the ways in which the 'Old South (Lorel)' is transfered to the 'New South(New Orleans)', and the two key characters which represent this old and new world (Blanche and Stanely respectively).
The war can be seen as a catalyst for the change from the Old to the New.
Examine the idea that the Old South created a veneer of respectability, when in reality this masked the true nature of that society.
Consider the quote by Stanley to Stella, "When we first met, me and you, you thought I was common. How right you was, baby. I was common as dirt. You showed me the snapshot of the place with the columns. I pulled you down off them columns and how you loved it, having them coloured lights going! And wasn't we happy together, wasn't it all okay till she showed here?"
That's just one idea, goodluck.