If drafty windows had you feeling the chill last Winter, use the temperate days of Fall to make your Winter indoor season more comfortable. Caulking sets better when it’s dry and temperatures are not freezing. Apply it before it’s too cold, otherwise it won’t stick properly. And don’t forget to weather-seal around doors too.
For windows that open, use weather stripping to seal the movable parts. If you want to get some fresh air in on a nice Winter day, be sure the seal stops air leakage but still lets the window operate freely.