How to wrap up the problem of keeping warm at home

The window frames in your house are getting old. There is only a single layer of glass, and lots of gaps around the windows and the frames. You can feel cold air round the windows in winter.

Do you: 

Make sure you close the curtains when it starts to go dark in the evening, to stop warm air escaping and cold air getting into the room?

Line the inside of the windows with clingfilm or bubble wrap to stop the draughts and prevent warm air escaping through the glass?