I've used this here to survive my own knife attacks.
situation: attackers left hand on shirt, next to neck, right hand knife, against neck.
If at all possible you want to avoid a strength battle, where it comes down to this guys brawn v.s. yours, cause chances are, if he's trying to gut you, he's confident he'll win. or on drugs.
defense: My right hand comes across and grasps his knife hand; important for hand to come across in between bodies. his instinctual response was to try to slit my throat.
next, duck chin to protect neck, (receive flesh wound on chin.. optional)
take the ever-present option in a male attacker, knee to crotch.
when his body recoiled away from mine, bend his elbow away from my neck using both hands.
Here's the complicated part. attacker is now hunched with right arm up in 90 degree angle. I have both my hands on his knife hand, with right on wrist and left on back of his hand. Apply pressure to bend wrist forward, fist will naturally loosen. Slide left hand down and remove knife from offenders control.
after that its up to you; the knife is in your control, the attacker is injured, possibly grounded.
i booked it.
This all to say, that when someone intends to mug you, they often don't announce it quick enough for you to adopt a defensive stance.
keep your center of gravity low and your arms free. in the case that you do become freed, you need to be in a stance that allows you to turn quickly and run.
A Chung-Do-Kwan Back-stance (two shoulder widths by two shoulder widths, knees bent, feet pointing perpendicularly away) works well for this while still allowing you mobility to convert to a more aggressive fighting stance.
Practice being able to adopt a stance that is comfortable for you quickly, and while someone may be restricting your movements.
the lower your body's center of mass ans the comfort of the stance for you are prime factors for defending yourself properly.
as for guarding major arteries, ducking your chin and lifting a knee to deflect are good things to be able to do on instinct.
you can take a knife to the thigh if needed. only hurts for about a month.