So here are a couple of elements you can add to a summer dress in order to make it more fall appropriate:
1. Tights or leggings: This is the most essential thing you need in order to make a summer dress more fall appropriate. The safe bet is to add black or brown, those always look great; but if you want to be more daring: add colored tights! An easy rule of thumb in terms of what color to choose is to look for a color in the print/design of the dress. That way you're sure it combines.