How to Sew a Button: And Other Nifty Things Your Grandmother Knew - something my grandmother gave me, even though she taught me most of these things growing up, it's a good book to have, especially since I can give it to L when she's older.
Start out searching for your perfect long maxi strapless turquiose prom dress by flipping through magazines and online to see what kind of dress you are most attracted to. Then hit the stores with an idea in mind of what you are looking for. Try on as many dresses as you can; your idea of the "perfect dress" may not be as well suited for you as another style. Don't limit yourself.