What is the best thing you can do for your home to save fuel?

Open the east windows of your home in the mornings and the west windows in the evenings. Also thick curtains are a good insulator. Reverse ceiling fans to blow upward and on the slowest speed. Good exterior door sweeps. Lower thermostat settings. Clean your burners on your heater. Inside and out. It is good to clean the burner jets. A clothes hanger works well. Blow out the burner with compressed air. Close unused rooms off and block drafts from under the doors with a towel. Also, at night you can place a box fan on the floor at the entrance of your bedrooms blowing out of the room and it will force the cold air out of the room and draw the warm air from the ceiling in since heat rises. I hope this helps. I am also trying to cut heating costs and these ideas have made a difference.

new insulation.

That is good over the windows, but make sure you have at least 1/2″ gap between the glass and the plastic, air is a good insulator. The distance between the screens and windows is a good one, I put plastic on my screens, that way, during warmer days, I can take it down to air out the house and replace them quickly.

Frilly and shear curtains look good but are terrible for insulation, hang some heavy curtains in the winter months.

Doors leak more than you think, a towel or anything is better than nothing. They sell those sliders to go under the door, but you can make your own cheaper.

You said fuel, if your using gas logs, depending on your style, do you need the vent open all the way, much of the heat goes straight up the chimney. I use a wood burner and the same principle apply.

Keep extra, unused rooms closed, only heat the most used rooms.

They have that dryer diverter that you can put on your dryer vent to reclaim some heat, at least while you do laundry. (see link).

If you have hardwood or tile floors, maybe get some throw rugs, only a little help but makes you feel warmer. That always helps.

Thats all I have for now.

Insulation is the obvious answer.Both loft and cavity wall insulation will give you the greatest gains. Close all doors,this helps with draft reduction.Use heavy lined curtains,even if you have double glazing, this helps with the cold spots that windows are.Fit a solid fuel or log burning stove so that the heat going up your chimney can be controlled as efficiently as possible.
Finally try turning down the thermostat on your central heating.Just a couple of degrees makes a world of difference.
I have successfully employed all of these and am saving a fortune.
Think of the planet.
Good to see you’re trying.
Good luck,
Masha.

If you thing all of your windows are tight, the next area would be under your outside doors. Are there any drafts coming in from them? Next would be your outside wall outlets. Remove the center screw and see how much cold air comes in from switches and outlets. You would be amazed at the amo9unt of cold air that can enter your home this way. Lowes and similar places sell insulation kits for these. You only need concern yourself with those that are on exterior walls. An outlet is about the same as a 1″ hole in the wall. These kits really do help and are inexpensive.