I think that causing your enemy to "bleed out" as quickly as possible is the goal of knife fighting. The easiest targets, like the femural arteries, the belly, where many organs can be reached, even the underside of the chin and the inside of the arms above the elbow are all prime targets that are best attacked from a low stance with an upward diagonal slashing or stabbing motion. Having a positive grip will ensure ones ability to inflict repeated stabs, perhaps into the abdomen, in order to cause as much damage as possible as quickly as possible, to end the knife fight that you don't want to be in to start with. Just my two cents...