Determine exactly what point you are going to make and write it down in precise terms. Think about why you want to make this point.
Develop a thesis statement (pages 47-49 in The St. Martin's Handbook). Then choose examples and details that count for something, those that move the reader toward some goal.
Choose the best examples that honestly reflect the group or class they represent. Do not pick examples that do not support your thesis. Also, make sure that your examples display all the chief features of whatever you are illustrating.
Do not give your examples and their details in a haphazard manner; give some real thought to arranging them in the best possible order. You may use order of familiarity, climax, importance, or some other order.
If an essay develops a single example, try to have at least three important things to say about it--three areas of discussion.