actually,
what i do is to cut the slots diagonally making sure the direction of the slots send the "rubbish" to the outside of the hub and not back into it.
i also give the both the lining and the pads a quick "whip" blast with a sandblaster as it takes any glazing off of both surfaces thus giving more grip. if that makes sense.
but then again, all my bikes are Yamaha's and thier brakes as we all know, work.
well lubed cable and actuating arm in the backing plate are also a must