In terms of handling:
1) Know where your blade is at all times...this may sound obvious but I have read so many stories about people who leave unopened blades on the table and "forget" about them until it is too late
2) Never underestimate the sharpness of a knife ("treat all as if sharp" so to speak)...some knives may feel dull to the touch but thanks to their edge geometry, they can sever an appendage if you don't give them the proper respect
3) always use a secure grip...the impact of stabbing, slashing, or chopping can wrench a knife out of your hand (or worse, make your hand slide down the blade!) if you don't hold on tight...in reverse grip, you might want to "cap" the butt of the knife with your thumb (especially if your knife does not have a guard)
You might want to consider "tip-down" carry because you are far less likely to cut yourself if the knife happens to open in your pocket.
In terms of knifefighting, to quote Mick Strider:
"Sharp, pointy parts toward enemy.
Safe warm parts toward self."
Another famous quote (or two):
"never bring a knife to a gunfight" or "the best knife to use in a knifefight is a Glock or 1911"
NEVER pull out a knife to scare/intimidate someone...speed and surprise are the best tactics for using a knife in self-defense
RL