I regard a repeating shotgun--either pump or autoloader, it doesn't much matter--as the best personal defense firearm available. Most personal defense emergencies, and nearly all self defense shootings that are later ruled justifiable, happen at short range. The shotgun is the best short range gun, so that is the gun to have. So runs my reasoning; it seems an obvious matter to me, but if you have a counter-argument, let me know in the comments.
The most evident difficulty is that the shotgun does not hold a whole lot of ammunition and its tube magazine must be reloaded with single shells, one at a time. That at least is what is most common. There are a few box magazine shotguns around and some speedloader gadgets for tube magazine guns. But in general, what people find most practical is a tube magazine and some sort of ammo carrier--a butt cuff, a side saddle, or a belt or a bandolier--that supplies you with single cartridges. This setup offers the minimum bulk of gun and gear, thus maximum maneuverability for the shotgunner.
"If you ain't shooting, you'd better be loading." So runs the time honored advice. You must replace the shells you fire with new ones inserted into the magazine. This continuous topping up of the ammo supply assures you will not be caught with an empty gun. "Shoot and move" becomes "shoot and move, while reloading the whole time." Ideally you reload before the gun runs entirely out of ammunition, rather in the way that you avoid overdrawing a checking account--put a bit in before it all goes out. If you always operate your gun that way, you will have no need for the distracting rigmarole of reloading the gun from its chamber-empty state. You will only need to poke shells into the magazine.
There is a pitfall that you absolutely must avoid when reloading. It is possible to load a shell into the magazine backwards, and the result is a jammed gun. You must verify, by sight or touch, that the rim of the shell is to the rear when you push each shell into the magazine. It helps if your ammo carrier (bandolier or the like) orients the shells so that they always come out of the carrier and into your hand facing the same way.
That brings us to the actual method used for reloading. There are several methods, but I always use the same one, for simplicity and consistency. I like the so-called violin method. (Directions are for a right handed shooter.)
I place the flat of the buttstock atop my right shoulder, with the gun's loading port, on the bottom of the gun, facing outward to the right. My left hand retains control of the forearm and keeps the muzzle downrange. My right hand pushes shells into the port, thumb on primer. This is very positive and simple and I have a good view of the shells and the loading port. If I need suddenly to put the gun back into action, I thrust the left hand forward, pushing the muzzle to the target. If there are shells in my right hand I drop them and take up a firing grip on the gun.
If you think the matter through, you will see that your sustained rate of fire is no faster than you can reload; the time it takes you to shoot one shell and load one to replace it thus becomes your basic measure of rate. For a brief time the shotgun can produce tremendous firepower, that is, for as long as the ammo in the magazine lasts, but when you must reload the rate drops a great deal. Thus you must budget your fire intelligently, using no more ammo than the occasion requires.
Fortunately, most real-world emergencies, as contrasted to 'practical' competition scenarios, are resolved without expenditure of a great deal of ammo. Lots of cops have done just fine using the standard Remington 870 with its four-plus-one capacity. The shotgun's effectiveness and hit probability are such that you will not often need a lot of shells. Still, we practice reloading as we shoot, getting ourselves into the habit of topping off the ammo whenever we get the opportunity, because "one never knows, do one!?"
Competition shooter Dave Neth demonstrates two loading techniques, the violin method first. You can also use the violin method to reload with ammo supplied from a belt, bandolier or other ammo carrier; you do not need to use the side saddle carrier shown in the video.