of rubbing alcohol on a wipe and gently wipe the gunk of the sticker and decals on your window. be sure to do it gently, especially if the glass is thin. hard cleaning might break the glass.
the obvious maintenance that any business owner should do is to dust it off regularly. use a small broom, a duster, or a vacuum to remove the dust and other debris on the corners of your windows.
water is known to cause rusting, especially if your window hinges and railing is made of metal. be sure that your window is dry at all times. after the rain, wipe off the excess water on the glass 