Keep the corsage in mind. Your prom date is responsible for buying your corsage, but you should talk it over with him beforehand so that he picks out something suitable. Also keep in mind that you'll need to buy him his boutonniere, and ideally, the two pieces should coordinate with each other.
Your corsage should complement the color of your dress but it should not be the same exact shade. Also, try to make sure that the corsage and boutonniere match each other in terms of color, flower choice, and overall style.