Maybe I shouldn't admit it but I never bother to ask, if a spot presents itself and if I need it that's where I'll camp. I have over time, developed my own criteria of what I am looking for and will modify my decision making depending on whether its out in the countryside or in a village type setting.
In the countryside I don't like camping in woods, I prefer a wall or fence behind me. I prefer to camp on the edges of fields with no cattle, sheep or horses around. I don't seek out wide open spaces either. I prefer to be a discrete wild camper.
Sometimes, like last year, if a gate separates two fields with no animals in them I have been known to open the gate to make a 'V' shape to the hedge or wall and bed down in the triangle. The last time I did this I found some privily branches to secure the triangle opening. I did this because I was concerned about the possibility of wild boar roaming around, I thought I heard something in the night but I suspect it was all in my imagination!
I have also slept on, hut wooden verandas, on the flat surfaces of farm trailers and once on a wooden door that had been dumped. The ground was rocky and stony so the door was a very useful find.
I always try to find a pub in the evening and if I do find one I explore the area around it to find a spot first. This can be on the edge of the local cricket pitch (very useful places) behind or to the side of the pavilion and all sorts of other flat 6' x 4' areas that may be available.
I then go to the pub for a meal and will return to my chosen spot at dusk, quickly and quietly erect my tent, get in, sleep, get up early, pack and away! I've never yet been disturbed once. I think I can now say that over time I have developed an 'eye' for such places, I now know what I like and what I will avoid. I do not camp in public parks unless I'm really forced into it. I've only done it once, just completely in the wrong place at the wrong time of day and in bad weather.