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.
4) Spray the windshield with Stoner Invisible Glass and wipe using the same process with the Waffle Weave Glass Towel.
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