When you have chosen your outside locations, revisit them with your art director, production manager and D.P. so that they can study them. Show them exactly where you want the action to take place. Sometimes a location has to be dressed. For Milos Forman, choosing the right location was just the first step. Then he would go to a great deal of trouble to repaint and alter it with the permission of the owners.
Costume designers are important people.
Don't ignore them or be content just for them to do their own thing. Instead, tell them the kind of clothes you expect and ensure that they remember that very bright clothing or white shirts can cause lighting and color problems and a change of atmosphere that you may not want at all. Have spare alternative costumes for your principal actors and actresses. In any case, you are not likely to want them to wear exactly the same clothes all through the film. Also, explain exactly how you will use the extras.