Glass cleaner on a paper towel, then dry paper towel. You have to use just enough glass cleaner–if you use too much, the dry towel won't be able to remove all the residue and you'll have to repeat. Or instead of repeating, sometimes elbow grease is enough to get it out–just keep rubbing with the dry towel (moderate pressure) until the streaks are gone.
If the window is clear then you could use most any household type glass cleaner. I can highly endorse the use of newspaper - will not streak and has enough stability to get into some tight spaces before getting saturated. However, I'd use caution in the event your case window is tinted. Not all cleaners are recommended for use on tinted glass. Read the label and see if it is safe for tinted glass.
Yep, i do the same.
Spray Windex on the window. Wipe the window down with paper towel until clean. Then quickly dry it off with a fresh paper towel before the cleaner starts to dry. If the windex starts to dry before you can wipe it down, reuse the damp paper towel to get it wet again. That's probably why your getting streaks, your cleaner is drying on.
Or you can always go the professional route. Spray it on, then squeegee that sumbitch!
Be sure to wear kid gloves when opening and closing from here on out or your right back in fingerprint hell