Malc,
It's quite simple:
There are two types of glass, hydrophilic and hydrophobic. Hydrophilic 'likes' water and the other doesn’t. Hydrophilic glass will allow the water to run off the glass as a sheet; the other just beads up and sits there !
With hydrophilic glass, wash as normal along the top edge, then down the sides, then all over. Then finally take the brush to the top of the glass and lift it away by an inch or two, this allows the water jets to rinse pure water over the entire glass, rinsing away any remaining dirt.
With Hydrophobic glass just wash and rinse well, and hope for the best !!! Some windows come out really well every time, others just never dry without leaving spots.
I must admit I plaguarised it; credit goes to Dennis Taylor from anotherforum!