This is simple and effective. I use an ammonia and phosphate free blue window cleaner that i purchase from the local dollar store for 99 cents. I crumple up some news paper, spray it with the cleaner and scrub the window with it. The fibers in the newspaper and the crumpled surface takes care of the dirtiest windows. I picked this up when i worked at a mall. Nothin' cleans snotty sticky kid hand prints better.
Step 1: BEFORE
Crumple up a sheet of newspaper and spray it with your cleaner and scrub your window. Next......
Step 2: AFTER
Next step, crumple up a dry sheet of newspaper and buff your window. Thats it.