It may not always be possible but the best idea is to try to fly so high as to stand a fair chance of gliding to an airfield. With a GPS you can get directly over an airfield without even being able to see it, or even if above cloud. A route like this is fairly easy if passing at a fair height across central and southern England.
Landing at a closed airfield in the dark is difficult but not impossible and you are less likely to hit wires or building than if you aim for any old field. I have done this myself and found it quite straightforward but the hands do sweat a bit. In the flare you can judge the height well enough to have a (hard) landing if you look out of the side window.
If you are unlucky enough to be flying too far from an airfield (although you do make your own luck to some extent) then I am certain that a well lit area is best. If you land in a controlled manner and then hit something then at least you will be found quickly which is what will make the difference.