If you plan on doing some window cleaning today, make sure it is dull, not so shiny day. Windows are much more likely to streak and look bad if you clean them in direct sunlight. That's because the sun will heat the glass so much so that it will cause the water in the chemical to evaporate too quickly for you to clean it off.
When you are window cleaning; use a squeegee to clean the excess water off. When you do this, hold the squeegee at an angle. The angle will allow the water to slide down the squeegee and to stay off the rest of the window in the process. This way, water only leaves the squeegee at the bottom end.