If you do decide to file on the nut slots, DO NOT make them deeper, only side to side. The strings usually bind at the back of the slot (tuner side). A small piece of 320 grit sandpaper should be all you need. Sand the side of the slot a tad in the direction of its tuner. A little can make a big difference. As others have said, use the self locking method with only one or less wraps after the "knot".