Single edge knives like the ones you find in the kitchen... should be pointed edge towards bad guy....
Most of the combat knives that I like are double edged. If your bad guy is holding one then hopefully you'll have a bigger one.
If you don't know how to hold a knife then don't get all ninja viking pirate on us... Just hold it as you would when cutting steak or chopping celery. Slashing and cutting is 90% of what you'll use it for... not thrusting.
PS I HATE when someone says to me "That's how they do it in REAL LIFE" LOL