Soak the glass with a foaming glass cleaner (not Windex). Most Dealers use 3M Glass Cleaner (part# 0888) ...use a single edge razor blade while the glass is wet.
scrape the entire windshield.
wipe clean then wet with water and apply Bon-Ami cleanser and clean.
clean wiper blades with alchohol. Keep in mind....products like Rain-X break down over time causing a residue.
Windshield glass is porous...the cleanser cleans the "grain/pits".
Reference: Service Bulletin- Jumping/hopping wiper blades."
Some believe in a vinager and water solution wash , drying with newspaper works....skip the newspaper,it leaves fibers in the glass.Use fiber free towels instead. All Rain-X does is "fill" the glass to create a more flush surface. Unless cleaned properly and re-applied regularly....it can do more harm than good.
Ever seen shadows left behind from a Used Car Lot's windshield paint?....it's because the glass "sucked up" the paint.
Reference: 20+ years Dealer Experience