Size, Shape, Surface, Surrounds, Slope.
The bigger the better, longest dimension into wind. Wide is good - bigger choice of final landing direction. Firm grass is best, not ploughed is good. No trees or cables on final approach is good. Slope - really hard to judge!
Night - best advice is stay above min abandon height and have a parachute. Failing that, turn into wind, get the flaps down and hope that when the landing surface finally becomes visible, it's not wall to wall barn!