You shouldn't use your build-in flash. Ever! It's sucks and it is always very obvious when people have used it. I only lights the closest foreground leaving everything else pitch black. In the Audi pictures you have white spots all over the car which come from reflections in the ice. You should always try to have another light source than a straight forward flash. A tripod and slow shutter would be what I would have chosen. Use the ambient light!