Article from The Daily Green
Instead of harsh chemical sprays, get those windows and mirrors crystal clear with a simple solution of white vinegar, newspaper and a little elbow grease. You'll also save money and the hassle of needing to stock more cleaning supplies.
It's simple: mix 2 tablespoons of white vinegar with a gallon of water, and dispense into a used spray bottle. Squirt on, then scrub with newspaper, not paper towels, which cause streaking.
If you run out of vinegar, or don't like the smell, you can also substitute straight lemon juice or club soda (don't dilute either in water), and rub with newspaper. See, simple!