If I answer the door ...
I have a gun in my hand behind my back, completely out of sight. If it's needed, I don't want to have to draw it, and I certainly don't want to show it. I can always shove it in a back pocket if that becomes advisable.
But I usually don't answer the door if I am not expecting anyone. The dog barks enough to give most people the idea they don't want me to open it, anyway. I think I missed out on a chance for Girl Scout cookies not long ago for not answering the knock, but such is life.
By the way, on the rare occasion that I do open the door to someone I don't recognize, I stand mostly to the left of it (the hinges are on the right) and open it with my left hand. If they did crash through the door, I would not be pushed off balance, but to their side or behind them, gun in a protected retention, point-firing position.