Ibsen's A Doll's House and Larkin's "This Be the Verse" are both about the unhappiness in families. This might be a point of comparison that you can make between both works. However, A Doll's House is about the deceit and misunderstanding between a husband and wife, while Larkin's poem is about the ways in which parents are flawed because their parents were flawed too.
In writing your thesis, you want to include both a comparison between the works (for example, that they both treat familial problems) and a contrast between the works (for example, that Ibsen concentrates on marriage, while Larkin concentrates both on marriage and parental relationships). Sub-points include minor points that you will discuss in your body paragraphs. These points might include how, for example, Ibsen portrays the flaws in marriage. In his play, Nora is the "doll"; her husband patronizes and treats like a child, while she, for her part, tries to deceive her husband about the money she has borrowed. Your other sub-points might include what Larkin expresses in his poem. Take apart each line and think about what he is saying about parents' relationships with their children. For example, he writes, "They fill you with the faults they had / And add some extra, just for you." What is he saying about the ways in which parents unwittingly pass along their flaws to their children? What does the metaphor "It deepens like a coastal shelf" mean in reference to families' misery? By answering these questions, you can develop sub-points in your body paragraphs.