The very nature of windows means that any dust, dirt or marks are instantly obvious for anyone looking in, or out.
So keep them clean like a pro with this handy guide.
What you will need
Start with all the right tools - the most important one you'll need is a quality squeegee. Preferably not one from a petrol station, but you can tell the best squeegees as they usually come in three pieces - the handle, the channel and the rubber.
You'll also need a bucket, a scraper, detergent or window cleaners (professionals disagree on the best option, so use whatever you already have!), and a 'mop' - otherwise known as a washer or wand - which is the part you use to apply the detergent and lift the dirt.
Of course, not all windows are at ground level. This is easily remedied however, with scissor lifts or man lifts to get you to the correct height.
The rest of the job isn't rocket science. Just fill your bucket with warm water (too hot and the water will evaporate off the windows too quickly) and a few squirts of detergent, and get going!