Process for Cleaning Extremely Dirty or Grimey Windows
1) Saturate the surface with Opti-Clean.
2) Spray some Opti-Clean on your towel. I really like the plush Door Jamb towel for this step.
3) Wipe windshield in an up-down, left-right pattern, then go around the edges.
5) Finish off with some Bead Maker n a fresh waffle weave towel. This will provide some decent water beading for a clearer window that’s easier to clean next time.
Here's a good video Matt did: CLEANING WINDOWS