One theme you could look at is what we live for, what keeps us going, what floats our boat.
Each of the characters in The Glass Menagerie live for something different, have different views of their lives, different, visions of the present the past and the future.
Amanda is worried about her daughter, Laura. She is concerned that, with her brother gone and she, her mother, dead, Laura will not be able to take care of herself. Amanda is afraid that Laura may not survive without someone to care for her. What Amanda lives for is the coming of a "gentleman caller" who will sweep Laura off her feet and take her away and love her and cherish her.
Tom lives for the possibility of something more dynamic than his daily, dreary, humdrum existence. He works in a shoe warehouse and desires desperately to get out of his present life. He wants to (and will) join the Merchant Marine and set sail for ports unknown... places that he hopes will give him freedom to search out romance and adventure.
Laura is happy with her old phonograph records and her collection of little glass animals, her glass menagerie. Hard as it may be for one to believe, polishing her little glass animals and making up stories about them is just about all Laura needs to make her content. Would she be any different if she had a real relationship with a gentleman caller? Maybe. But her glass collection fulfills most of her needs.