Clean on a cloudy day. Direct sunlight dries cleaning solution too quickly, leaving streaks behind.
Use a microfiber cloth or squeegee instead of paper towels, which can leave lint and streaks.
Clean in a consistent direction — horizontal strokes on the outside, vertical on the inside — so you can spot which side a streak is on.
Don't forget the frames and tracks; dirt here can wash back onto your freshly cleaned glass.
For hard water spots, a vinegar-water solution can help break down mineral deposits before your next professional cleaning.
