Generally I try for a pull thru parking spot, two open slots that are head to head and I park in the center of them. If the store doesn't like this then they should have bigger spaces since so many people drive p/u these days. I do my best to avoid backing out of a space, that is a hazardous maneuver with the terrible back end visibility. With the new trucks having back end cameras this probably isn't as much of a problem. If I can't find a pull thru then I'll back into a space (or two) which is safer. Angle spaces are also good.
I have a back up camera that I need to install as soon as I figure out the no label wiring diagram.