best way to clean inside of windscreen

First, dry-wipe with a clean microfiber to evict dust and that mystery film. Then hit it with an ammonia-free glass cleaner or a 50:50 isopropyl alcohol–water mix, spraying the cloth, not the glass. Work in small sections using tight circular motions, then finish with straight horizontal strokes for a streak-free smug glow. For the outside, finish vertically so you can spot which side misbehaved. Avoid paper towels (they shed) and anything oily that turns the glass into a nightclub haze. Do this and night driving won’t feel like peering through a chip fryer.