There's this Japanese word "mottainai" which was used on an almost daily basis when I was growing up. It means "don't be wasteful", particularly with regard to "stuff" and energy. This is a page of links to energy efficiency advice. I'm trying to favor pages with info on using less rather than buying more efficient appliances.
9 Ways to Save Water with a Water Heater
72 Ways to Save Money on Electricity Without Spending a Cent
Insulation and Sealing Air Leaks
5 Ways to Insulate Your Windows for Winter
Some tips that I haven't put on pages, yet.
Use plastic taped or glued to window frames to trap air against the window. This prevents heat loss to the cold glass. I used laminate floor underlayment, which is a plastic foam sheet.
Window film will slow down heat transmission through the glass as well. The slightly reflective type will also reflect sunlight back out, and keep the house cooler in the summer.