Methodical definately. I helped the OH wash her car yesterday morning and as I was washing one side she was doing the other and what she did was do the roof her side, then the windows then sort of moved round to the front wing without doing the doors...WTH?
Needless to say I told her off. She said she was going to go back but what's the point in that? It takes longer to retrace your steps and you're more likely to miss a spot.
Anyways, the point is to do it in relative sections like do the whole roof first, then whilst on one side do the whole rear quarter/rear door from the tp down, then move over a step and do the front door and skirt from the top down etc etc....
It's like wheels, start at one spoke and move your way round. I've seen some people clean one spoke and clean the third next spoke, then do the opposite spoke at random and wonder why they're missed some.