There are many different trains of thought for this type of thing, and they range from the super simple to the "hollywood" tactics (i.e. really flashy, but no substance).
I am not the guru as far a bladed weapons go, and I tend to take the very simplest approach as far as using them as a defensive tool. My first preference is to use a sidearm if at all possible. Bladed combat is tricky, and you usually have to strike many, many times with a blade before you stop the threat (prepare to be injured yourself).
With that said, I believe it's still important to incorporate a blade into your defensive practice routine in some shape or form.
The first picture is an example of the "higher end" pair and the "lower end" pair. The difference in looks and monetary cost is great, but they will both do the same exact things.
This is a basic stance with the "high end" pair. I like to call these stances Double Jeopardy. The reason is if the threat gets really close and the pistol fails, I have the blade to slash at any open areas (i.e. arms, face, neck, chest, stomach, groin, etc....) that the threat will expose.
P.S. As a general rule, it is better to slash then stab. The more "fire hoses" you cut, the more the liquid the threat will lose.
Here's the same stance with the "low end" pair.