Once you have narrowed your choices to one particular prom dress style, try on that style in a variety of different colors and finishes, then make your decision.
Try on dresses in a variety of different styles and cuts to find the one that works best for your body. You should already have done the work on the body shape, but here are some additional considerations:
If you have a slim figure, you may look best in a sheath prom dress that shows off your silhouette.
If you are curvy, you may want to consider an A-line prom dress that will highlight your waist and minimize your hips and thighs.
If you're short and petite, dress shopping may be more challenging; cocktail dresses become full gowns and party dresses become cocktail dresses. However, with plenty of time ahead, you can get these tailored to your size.
If you're looking for a longer dress, look for a short dress that is long on you. It will fit better and will fit you everywhere else without being too long.