from behind, holding the knife in an "icepick" or reverse grip,hold your hands sort of like a rear headlock-say, right knife holding arm arond neck, and grap top of hand with yor left from other side, tuck your head into his back and pull down,driving the blade (behind the collarbone) into subclavian artery. Kick out the back of the knee but it isn't required.
Getting from A to B is varied. You can use the knife as a "mantis hook" to the attacker's arm,break it, or at least hyperextend the joint, and come right up-there are many areas to strike on the way in, such as across the carotid. You can hook the neck, pulling his head down,and then run the blade around. We used to call this "The Sayoc Smile"-because it was a fave of Chris Sayoc's.