Dave,
Like the professionals you can buy a squeegee and a lambs wool scrubber that goes on an adjustable pole at a decent hardware store or were janitorial supplies are sold. Use the soap specifically intended for window cleaning, I am not sure why but it works better than other cleaners I have tried.
I tend to leave streaks with the squeegee so my little window cleaning trick is to use a drywall pole sander and a micro fiber cloth folded in half. Lightly spray the cloth with a 50% mixture of alcohol and water and polish away. If the windows are really bad I will wash them down outside with a bucket of soap and water using the lambs scrubber on a pole and rinse with the hose. When they dry I use the micro fiber cloth on the drywall pole sander, microfiber cloth and alcohol to polish them up. I also do this inside on two windows that are in dormers in our living room that are 16' off the floor.
Rege