I think that one of the main things Norman Jean's and Leroy's relationship suggests about what is needed to keep a happy marriage is communication. In the ninth paragraph of the first section, the author describes one of the few moments when the two do manage to connect, saying,
"When she explains to Leroy the three stages of complexion care, involving creams, toners, and moisturizers, he thinks happily of other petroleum products - axle grease, diesel fuel. This is a connection between him and Norma Jean".
Aside from that, Leroy and Norma Jean never seem to be able to penetrate beneath the surface in their interactions. In the last three paragraphs in the third section, Leroy thinks,
"He wanted to know what she thought - what she really thought - about them",
"They have known each other so long they have forgotten a lot about each other".
Leroy is aware that he and Norma Jean have lost the ability to communicate entirely. In the ninth paragraph in the fifth section, the author says,
"Leroy has the hopeful thought that they are sharing something, but he knows he is a fool to think this",
and, in the ninth paragraph of the last section, Leroy admits,
"They are still just making conversation".
There are other issues between Leroy and Norma Jean which prevent them from having a good marriage, especially the question of individual identity. Communication, however, is still inarguably a basic element to ensure a happy marriage.