The content of the soapy water, the tools and the way you wash your windows contribute to cleaning your windows without streaks.
Mix an onion, washing-up liquid, cleaning vinegar or HG window cleaner with lukewarm water.
Wash your windows with a clean sponge or mop applicator.
Clean and dry the window frames.
Use a good-quality squeegee.
Dry the windows with an s-shaped motion.
Wash your windows in the shade or in the rain.