Get a pitcher of lukewarm water and splash it over the windshield. (Don't do this if it is very far below freezing outside, however..it will make it worse)
Whatever you do don't use salt on you windscreens. It will be splashed onto the paintwork & it will rust very quickly.
You've all seen the cars that live at the seaside.
Scrape ice/frost off with a credit card type of card or a proper ice scraper (I have used a plastic fish slice before now though) as sometimes if you use de-icer it can freeze up again. Scraping it off gets rid of it better, put your car heater on while you are doing it. My husband however starts the engine with spare keys, locks the car, has a cup of coffee then goes out to car to drive to work. I think this is an awful waste of fuel and dread it disturbing our neighbours so I wouldn't follow this. My old house had a garage actually big enough to put a car into, that made a huge difference!! No scraping ice, snow or anything - brill.
Aquire sturdy plastic scraper with strong handle and good tough surface for windscreen. Start engine and turn heater to max with blowers directed on screen. Switch on heated rear window. Make positive long strokes along window parallel with roof working your way down to bonnet. Repeat operation standing on other side of car. Take your time doing this as blowers should assist in melting the ice as engine warms up. Should only take 5 mins or less. Never leave the car on its own with engine running!
If you know its going to be a cold night apart from covering your windscreen what works really 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 in the evening