When I install new brake lines, I very gradually tighten them up in order to feel the flare end of the brake line squish to match the contour of the fitting. I then loosen it and re-tighten it. You should notice that it takes less turning the second time.
Doing it this way will prevent over-tightening and stripping anything, or galling the flats where the wrench contacts the nut.
Carl
