Most uses of knives are more like surprise attacks or using a knife on someone who is unarmed.
Probably the first rule of effective uses of a knife is to keep it hidden. If you are up against someone with superior weaponry, strength or size, if deadly force is justified, do not give a hint that you have the knife until you employ it, rapidly, ferociously and repeatedly.
I gave my daughter a knife, and said if she ever had to use it, use it fast and hard against effective targets to disable your attacker; once you get free, flee so that they cannot grab you.
There are numerous books and videos on knife fighting. My favorite is “Knives, Knife Fighting, & Related Hassles How to Survive a Real Knife Fight” by Marc “Animal” MacYoung
If you decide to show the knife, (deterrence is more likely than any other reason) learn one or more fighting stances. Keep the knife back near your body so that it cannot be easily kicked or knocked away. The other hand should be used to protect the knife hand.
At least you want to *look* like you know what you are doing.
Marc “Animal” MacYoung is a real deal knife instructor who learned his trade the hard way.