Points to consider before planning a US vacation:
Weather: Since the U.S. is so large, most visitors will have in mind a number of specific destinations to visit before planning a trip. The best way to get tourist info is to visit the tourist boards for the individual states or cities, as there is no centralized tourism site for the entire country.
Clothes: This very much depends as to the area that you're going. Check out the average temperature for the time of year that you are likely to be going.