If you heat with electricity and live in a warm and sunny climate, consider installing a solar water heater. The solar units are environmentally friendly and can now be installed on your roof to blend with the architecture of your house.
Weatherstrip and caulk all cracks between the wall and the window trim, especially under the window sills. Replace broken glass and putty any loose window panes. Caulk around the moving parts of windows with a strip-away, non-permanent caulk during the winter. This type caulk can be removed easily in the spring.