I'm already on record as saying that reading, watching videos and range practice on your own or with a couple of friends is no substitute for formal training with a good instructor. For years my wife and I have had people say, "Teach us to shoot." Most of the time what they are really asking is, "Teach us to fight with a gun." There are some substantial differences in skill sets involved. Of course, a person needs training in safe gunhandling, loading and unloading, and safely and successfully discharging rounds downrange and hitting their target. But those skills are not really enough if a gunfight is in the offing.
There are some excellent books and videos available that will help with the gunfighting part of the problem at hand. I am of the opinion that, safety matters excluded, there is no one single solitary true path that every shooter must follow on the road to becoming a more accomplished gunfighter. There are many excellent instructors teaching today, and not every one of them teaches exactly the same thing. All of them I am familiar with will tell you to seek training from other instructors, to take the elements of all the training that suit you best, and use those which work best for you in developing your own system of the tactical application of whichever weapon you are using.
There are a handful of people who are better known as proponents of the shotgun. Perhaps the best of the bunch is Louis Awerbuck. The diminuitive South African has been teaching on the road for 18 years now and has been training others for some 30 years in fighting with firearms. Louis' books and tapes are listed on his website at
http://yfainc.com/books.htm . He insists that people not buy his first book at this point, stating that too much of it is now out of date, but any of the others will be useful.
I'd also recommend Jim Crews' _Some Of The Answer, Advanced Urban Shotgun_ which you can find at
http://www.marksmans.com/id13.html .
Another useful title is John Farnam's _Farnam Method of Defensive Shotgun and Rifle Shooting_, at
http://www.defense-training.com/pubs/riflbook.html .
Gabe Suarez has written _The Tactical Shotgun_, which you can see at
http://www.booktrail.com/Guns_Shotguns/tacticalshotgun.asp among other places.
Chuck Taylor's book is also available there-
http://www.booktrail.com/Guns_Shotguns/combatshotgunandsub.asp .
I have copies of the above and can recommend them, of course there are more books and tapes out there I am not familiar with. And some of the better shotgun instructors like Randy Cain have yet to put pen to paper as far as I know. But this list should give you a good starting place for study, and I hope it will lead you to select one or more of the authors to train with in person.
Do keep in mind that the state of the art is a constantly moving target, that no one person ever knows it all, and that some of the shotgun gaming hardware and software (3-gun etc.) do not necessarily translate all that well to the street- or the hallway in your home at 2AM. The closest you can get to a gunfight is training with a good gunfighting instructor who knows how to get you to bring increasing amounts of pressure to bear on yourself while running your gun, shooting appropriate targets with proper ammunition, avoiding no-shoots and moving all at the same time.
lpl/nc