Streaks come from two things: residue and drying. Household glass cleaners leave a film of surfactant behind, and paper towels shed lint and smear it around. Cleaning in direct sun makes it worse because the solution dries before you can remove it.
Professionals use a squeegee, a small amount of dish soap in a bucket of water, and a lint-free towel for the edges. The soap loosens grime, the squeegee removes all the water in one pass, and the towel catches the drips. For exterior glass on taller homes, a water-fed pole with purified water rinses the pane and dries spot-free without any wiping at all.
Around Puget Sound, exterior glass picks up a film of pollen, road grime, and, near the water, salt. It builds fastest from March through June and again after the fall rains start. Most homes look noticeably better with an exterior wash twice a year; storefronts with street-facing glass usually want it monthly.
Frames, sills, and tracks matter as much as the glass. A pane cleaned above a dirty track looks unfinished within a week. When we clean windows we do tracks and sills first, then the glass, then check every pane in daylight before we leave.