What A and J said is so true; although you haven't specified, I'm guessing white UPVC frames and here's my thoughts.
Last done trad and not for a while. Frames filthy. Vents filthy.
Trad will mean that soapy residue will be "pushed" into the seals between the glass and the frame and will remain there until rinsed out.
Filthy frames - especially those above - will mean that it only takes one run of impure water (due to water mixing with a bit of dirt from where the top frame meets the brickwork) dripping down and causing a run or spots.
Vents - these are the daddy of all the causes of runs and lines of spots - there are two ways of dealing with them thoroughly on a new clean.
On upper windows - go round every top window starting with the upper frame and vent and wash and scrub thoroughly including the upper seal and then quickly wash the rest of the window.
Go back to the start and you will probably see little black dribbles below the vents to the glass. Wipe these away on very low water pressure and then thoroughly side frame, glass and cill.
On lower windows you can do the same but if you can reach the top frame by hand then it will be quicker to wfp the top frame then go back and use a cill towel to wipe away the runs. Then do the rest of the window as for the upper windows.
It takes time, which is why you should always charge more for a first clean and do a good job rather than say to the custy it will be 2 or 3 cleans before it comes good. (IMO) Then next time you can fly round.
My fee is a pint of Wadsworth 6X of course!