Here's some basic
advice that hasn't been offered yet.
Always assume your opponent is a better fighter than you.
This ensures you don't underestimate your opponent. It's impossible to tell how good a fighter is just by looking at him/her. For instance, I just saw a pretty little 14 year old girl beat the snot out of my entire college
kali and
eskrima class. Turns out she was the instructor's niece, but no one knew that at the beginning of class.
I asked my teachers about the suggestion of holding the knife in your weak hand, and punching your opponent while they're watching the knife. Their response was there's no way to tell if your opponent is an amateur who'd watch the knife, or someone skilled enough to slice that arm to pieces as it comes in for a punch.
So,
Always assume your opponent is a better fighter than you.
I agree with a lot of
Doughbelly's advice.
Knife fighting is not something you are going to learn in front of a computer screen. Don't take my advice: go out and take some classes from a professional.