Whatever you do don't use salt on you windscreens. It will be splashed onto the paintwork and cause rust.
You've all seen the cars that live at the seaside.
If you know its going to be a cold night what works really well is to give your windscreen a wash of vinegar and water. This helps keep the ice from clinging but you would need to do it the evening before it freezes.
Get a pitcher of lukewarm water and splash it over the windshield. Don't do this if it is very far below freezing outside because it will only make it worse.