I am reading "The Self-Sufficiency Handbook" by Alan & Gill Bridgewater and am getting so much from it.
The chapter on self-sufficient houses has this list for improvements:
1 -- Fit good heavy curtains to all the windows and exterior doors. Open the windows during the day and close close them at night to keep the heat in. Wear layered clothes when the weather is cold.
2 -- Replace all single-pane windows with double- or even triple-glazed units.
3 -- Reduce the number of exterior doors.
4 -- Insulate the roof space and all cavity walls. If you have solid walls, add insulation to the inside or outside faces.
5 -- In the northern hemisphere, reduce the number or size of north-facing windows and increase the size and number of south-facing windows; vice versa if you live in the southern hemisphere.
6 -- Install a woodburning stove, and remove items like electric gas and electric fires. Fit vents and ducts so that you can channel excess around the house.
7 -- Fit a glass house, glass porch or conservatory over every exterior door. Fit vents at floor and ceiling height, so that you direct hot air from the glass structures into the house, and so that you can create a cooling circulating system.
8 -- Fit solar collectors on your roof, so you can preheat your cooking and heating water.
9 -- Modify your water system to save and reuse 'gray water', so you can use your bath an shower water to flush the toilets.