You might want to start by deciding what characteristics you are going to discuss in the body of your essay. You should probably devote one paragraph to Daisy's upbringing, since it influenced who she became. Growing up as a rich, attractive socialite living in a town full of young Army men who were eager to have her company shaped her attitude toward life and the types of activities she enjoyed. She also grew accustomed to men reacting to her in a particular way and she learned a certain pattern of responding to them during that time.
The officer looked at Daisy while she was speaking, in a way that every young girl wants to be looked at some time...It's a great advantage not to drink among hard-drinking people. You can hold your tongue, and, moreover, you can time any little irregularity of your own so that everybody else is so blind that they don't see or care.
Your second paragraph might address Daisy's marriage to Tom Buchanan. You could explore their relationship to each other, their relationships to their friends, the ways in which they protected each other. and so on.
Your third paragraph could look at how Daisy's relationship to Gatsby developed and died; how it was idealized in Daisy's mind at first and how it was abandoned in the end.
They were careless people, Tom and Daisy-they smashed up things and creatures and then retreated back into their money or their vast carelessness, or whatever it was that kept them together, and let other people clean up the mess they had made...
Once you decide exactly what you are going to say in the body of your paper, your introductory paragraph is a preview. It sets the stage by briefly introducing each of the three main points you are going to present in the body of your paper. Your conclusion is a summary, reviewing the points you have made and stating any overall conclusion you have supported about Daisy's personality.