I have a few ways of focusing in the dark.
1. If I can find something that is at least barely visible enough to use
AF I AF that bit of light and then turn of AF.
2. If there is not enough light I simply set the lens manually to the
approximate distance - sort of like working with the old rangefinder
cameras... or my old Rollei 35, on which I learned to guess distance
fairly accurately.
3. It helps that I often use a wide angle lens; it tends to be more
forgiving of slight focus inaccuracies.
Dan