The straight pull is the one everybody starts with. Wet the glass, place the squeegee at the top, pull down in a single steady line, wipe the blade, overlap the next pass by an inch. It is slow, it leaves a line at the bottom you have to detail, and it is almost impossible to get wrong. For small panes, Georgian bars and anything awkward, it is still the right answer.
The fan is what you graduate to. One continuous movement, the squeegee turning through the pane so the water is pushed ahead of the blade and off the bottom edge in one go. No overlap lines, no bottom detail, roughly half the time. On a big picture window a good fan is genuinely satisfying to watch and takes about four seconds.
Why the fan goes wrong
The mistake nearly everyone makes learning it is going too fast. The blade needs to stay in contact and the wrist needs to lead. If you rush, you lift a corner, water runs back behind the blade and you have made more work than the straight pull would have. Practise it on a patio door in your own house until it is boring.
Blade condition matters more than technique. A rubber that has been sat in a bucket curling at one end will streak whatever you do with it. Turn it, and when both edges have gone, change it. A new rubber costs less than the ten minutes you will spend detailing a window you have already cleaned once.
Scrim or microfibre for the edges is personal. I use scrim because it holds more water and I like the weight of it, but a decent microfibre folded into eight gives you the same number of clean faces and dries faster in the van. ▪