How do you get streak-free windows and mirrors?

Usually best results are achieved by using a glass cleaner product such as Windex. You can use a paper towel or other lint free cloth such as a old t-shirt. Most times for things like a mirror, a couple sprays will do the trick. For larger surfaces that tend to have more dirt, spray cleaner evenly over the surface. After spraying your surface, take your paper towel or lint free cloth and wipe the surface until dirt is gone and surface is dry.