Avoid using glass cleaners that are based in ammonia or alcohol. They may seem like they’d produce a more intense clean, but in reality, they can leave streaks and even a thin film that attracts dust and moisture. If you have an especially difficult spot, you can start your cleaning process by applying a solvent like acetone or rubbing alcohol to a clean cloth and rubbing it directly on the spot. Wipe it dry and then continue to clean your window as you would normally.
No matter how stubborn certain stuck-on materials may be, never use a razor or any other kind of blade to scrape them off. This can cause permanent scratches and leave your windows more vulnerable to breaking in the future.
Use a soft, lint-free wipe when rubbing the solution. A microfiber cloth is ideal but a gentle and clean paper towel can work as well. Rub from multiple directions to help avoid streaking.
If you find that you still have streaks after you’ve cleaned your window, simply rinse with clear water to help remove any of the remaining cleaning solution.