Take up knife defence class.
The best way to fight someone armed with a sharp weapon is to
either use a long blunt weapon or use another sharp weapon.
In knife to knife combat, keep your armed hand back and use your
other hand as a shield. Go for cuts, not stabs. Always look out for
opportunity to disarm opponent, e.g. slashing his armed hand or
slapping it out of his hand. Lastly, never be afraid to use your
defensive arm to protect yourself. It will end in a bloody mess,
but if you stick to some of the tips i've suggested, chances are
you will live.
Anyway, this is just a short summary on stance and techniques. You
will need real classes if you want to engage in knife to knife
combat.
