A number of the car parks I choose, have bays with hatched lines where you are not supposed to park, I normally put a tyre width into these giving me extra room.
Although yesterday when I took the car for a service, I stuck it in a completely hatched area as I couldn't fit in any spaces! When I came back to get my car they put it at the front door with no other cars near it ... nice
I've also chosen end spaces, meaning only one side of the car is exposed, then park as close to the edge as possible (without wheel scuffing).
The biggest problem I have is the length of my car, the front or rear normally sit way out in the open.