The overwhelming majority of people carrying a gun for self defense would do well to sell one of their guns (because damn near everyone owns more than one) and use the money to buy tuition to a class containing SouthNarc's Managing Unknown Contacts presentation. He's even put it on a DVD you can buy from Shivworks' website.
Being able to shoot well is a part of self defense...not the whole. Learning how criminals operate, learning to spot the warning signs of an impending attack, and knowing how to avoid placing yourself in a vulnerable position in the first place should be the focus of a deliberate effort to build knowledge and skill for every individual, but especially those who have a firearm for the purpose of self defense. The fundamental truth about criminals is that the majority of them are ambush predators looking for easy prey. There are some very basic but very effective things you can do to A. avoid the ambush and B. communicate to the bad guy that he's trying to tangle with somebody who has big, sharp fangs. The combination of that has a tendency to make most bad guys decide that they'd probably be better off selecting another target.
Being the best shot in the world is great. Having a huge gun collection is great.
...but it's not much practical good if you don't know how to read the world around you to see a bad guy sizing you up for an attack. People often talk about SHTF on gun boards. I have news, folks: SHTF doesn't mean some sort of zombie apocalypse or total breakdown of social order. It means some hammerhead(s) out there smoking a rock and then deciding that he's going to come after you and your family to get what he wants. The skill to shoot that guy in the face is certainly a wonderful asset on it's own, but it will work best for you when paired with the situational awareness and street smarts necessary to spot an attack before it gets to the point where there's a guy punching your face in.