Seal the cracks at the bottoms of doors by filling socks three-quarters full of sand or cat litter, knotting the tops and laying them along the bottom of the doors. Decorate them as mice or dogs.
If you don't have double-glazing, insulate windows in winter by taping clear plastic - even plastic film - to the frames. If you play a hair dryer over plastic film, this will shrink it slightly and smooth out any sagging wrinkles.
