So there are various window cleaning supplies on offer at your nearest supermarket, but if that's feeling too cleaning product-y for you, or whatever, be aware that you can also clean glass with pure oxygen plasma. Sure.
Available at your local Teso, or okay yeah maybe not, Ben Krasnow uses a vacuum chamber, a mechanical pump, and a radio frequency transmitter in his setup. The RF power ignites air plasma and can turn air or pure oxygen gas into the ultimate magnetic-wave-microscope-slide-cleaner. We all have microscope slides that need polishing, right? Right.