This is an excellent device for introducing conflict and exposition. In the first moments of this play we learn about the landlady, the protagonist, and their relationship. The bonus is that we are immediately propelled into the action. People have to be interested in what is happening to really hear what you want to say. Get your audience into the action quickly and keep them there.
Characterization is crucial.
Always remember that motivation is the key to strong characterization. Your characters must have a strong want or need that will enable them to take risks to get what they desire. Profile your characters before writing, so that you know them intimately. As a writer, you are in essence creating a life. Just as you would with your own children, you must allow them to be themselves.