Being as I've just learned of Jeff Cooper's passing, I will mention a passage from, I believe, Art of the Rifle that is to the effect that a man must fall a bit in love with his weapon, if he his to be maximally effective with it. I believe that the idea is that, if you really appreciate the weapon, you will be more inclined to handle it, practice with it, and generally become familiar with it. And of course, having confidence in your firearm of choice may make all the difference in a tough situation.
For me, that means a blue steel revolver, preferably made by S&W back in the "good old days". For the next guy, it may mean the latest 1911 from Bill Wilson, or a fine SAA with a touch of scrollwork, or even a Glock with a New York trigger and skateboard tape on the grip. <edit> Or even a Browning!
I know without the "Mine's better!!!" debate we'd all be pretty bored here, but all kidding aside, I really do believe it's a matter of falling in love with something and then practicing constantly.