For me - good rinsing is the key to leaving the windows as clean as possible. Only one (minor but justified complaint in 5 years WFP).
I also spend a lot of time on the first clean - it pays dividends in the long run. If they are particularly bad, I try to connect to the customers outside tap and give a good scrub and rinse with that. Saves wasting pure water if you have limited supply due to transport size.. I then go back to the first window and clean in the normal way with pure water. This works well for me.
If you make a good job of the frames to start with they only need a quick brush on each visit to keep them from building up with more dirt. If you don't keep them reasonable, after a while you will end up in the same situation as when you did the first clean.
Hope some of this helps you mate.