Always use the right tools! Professional grade squeegees, soap and applicators will give you the best sparkle!
If you want to clean your windows like a professional,
here are a few tips:
Always start with a clean scrubber or sponge and remember to rinse frequently if you are cleaning many windows, especially the dirty ones.
NEVER wash your windows in direct sunlight. If the glass is too hot it can cause all sorts of streaking problems.
Hold your squeegee at an angle so the water runs down the glass. You don't want water to be flowing from both ends of the squeege. Horizontal squeegee strokes will always work best.
Practice with the squeegee when you first purchase one; as it may be hard to control. Most professionals use an 18 inch model but you can start off with a 12 inch model until you are more comfortable.