How to Clean Windows
The secret to getting clean, streak-free windows is having the proper tools. Invest in a good squeegee, a strip washer (soap applicator and agitator) and dry cleaning cloths. Pour your preferred cleaning solution into a bucket. Dawn will work. Make sure the bucket is wide enough for the applicator to fit into. Scrub the window with the cleaning solution over the entire surface of the window. White nylon pads are great for getting the stuck on debris without leaving scratches. Squeegee clean and then use the dry cloth to get any leftover water or smudges.
For construction debris you may need to scrap the window with a metal blade prior to scrubbing as you do not want to push concrete splatter into the glass and leave scratches. Be careful using scrappers though since the glass my be scratched. Test in an inconspicuous place first. DO NOT use a scraper on energy efficient coated glass. These days the coating is often found on the outside faces of the glass in addition to the inside of a double paned window.