A good place to start would be to focus on the central character, Elisa Allen, and her personality traits. This of course needs to be linked in with the description of the setting that we are given at the beginning of this excellent story. You might want to start off the discussion then by asking what links there are between the setting as described in the first paragraph and the central character.
This will hopefully lead on to a discussion of how important the chrysanthemums are to Elisa, and then the all-important question of why Elisa felt the compulsive need to reach out and touch the gypsy man's ankle. What you are looking for from your class is evidence that they are able to link these different bits of information together to establish how Steinbeck presents Elisa as a lonely, empty character desperate for human contact and appreciation. Lastly, if they haven't discussed this already, you will want to ask your students about the symbolism of the title: what do the chrysanthemums represent?