Special K, The best instructor I have seen in person also makes and sells nets. He also sells a video with instructions on how to throw a net. At one of his demonstrations he explained the different parts of a cast net and why his nets were made the way they were. He did state that a net that is not made correctly can not now and never will be thrown correctly. He explained about different nets for different water depths and different nets to catch different bait fish.
His web site is
http://www.westcoastnets.com/ and you can e-mail him.
I have practiced some the way he tought us to throw it, and wile I am better than I was by a long shot, there is still more practice needed.
Good luck,