Insulate the Walls with Books (not literally):
Tall bookcases, filled with books add heat flow resistance to a wall. Move bookcases to exterior walls to slow the transmission of your precious heat from inside your home, to the outside, and to prevent the cold from creeping in.
Arrange Your Seating Away from Windows and Drafts
Place your couch and chairs where you can see the windows but not feel any radiating cold. If you're close to a draft, you'll be tempted to turn up the thermostat, even if the average temperature throughout the space is warmer than where you're sitting.
Take Care to Not Obstruct Air Ducts
Though the optimal placement of your sofa might be over a heater vent, know that placing anything over a vent will slow the flow into the room. Also, much of the heat might be absorbed by the sofa and instead of heating the room, you'll only heat the seat.
Wall Art Helps Insulate Too
Whether it's a quilt hung on the wall or some large picture frames, they'll have slow the transmission of heat/cold on exterior walls.