George Digweed's "Guide to Perfection in Sporting Clays" gun down, instictive method favored in the UK, and by SxS.
Dan Carlisle & Ed Arrighi teach pull away shooting in their "Secrets of the Triangle," combines classroom and video.
The excellent book by Chris Batha, "Breaking Clays," prompted me to order his video which has not arrived yet.
I have not yet seen any of the videos from the OSP School by Gil and Vicki Ash, but their books are outstanding....
Reading books and watching videos continues the quest, becaause IMHO there is no such thing as being too good a shot. Working with several professional instructors over a period of two or three years was what I used to establish a foundation. This work included experimenting with different types of guns, being measured for gun fit with a try-gun by two different experts (and checked again by four others) as I continued to refine my technique, and having the stocks on my guns altered to fit better than a glove: now where I look, the gun shoots (mostly). Oh, yes, and practice.
Lots of practice.
Hope this helps. Shoot Safe, SidelockSxS