And old show car trick is Bon Ami cleanser. DO NOT USE ANY OTHER COMMON ABRASIVE CLEANSER. Things like Comet and Ajax will scratch the glass. Wet the glass, sprinkle a dusting of Bon Ami, use an old T-shirt scrap or similar soft cloth and scrub. Rinse and you're done. Follow up with Rain-X and the wipers will work better.
Bon Ami has been around a long time. It's logo is a chick standing in front of a cracked-open egg with the slogan "Hasn't scratched yet". If you know anything about chickens it makes sense. Some more urban types are often left scratching their heads.