The safest, cheapest, most effective potion for window cleaning:
No need to purchase ammonia-based products, including some Windex products. You already have what you need in your own kitchen. Just a few drops of dish soap in a bucket of water or spray bottle, a good-quality squeegee, a sponge and a lint-free cloth is the kit you need to safely achieve sparkling windows.

Working from top to bottom, apply the solution to the window with your moist sponge. Next, go to town with the squeegee, wiping the blade with each pass. Finally, polish off any remaining moisture with the dry cloth.