Practice, take up clays, hunt birds, become one with your shotgun. You can learn tactics from a class, but nothing replaces experience and shooting flying objects for marksmanship IMHO. Take a "shoot where you look" class, some marksmanship training in addition to the tactical stuff if you don't do clays or hunt birds or something. Even if you do, it can't hurt.
I don't worry much about the tactical training with a shotgun. Mine is only for my bedroom/safe room. If he breaks through the door, he's dusted with buckshot. Pretty simple, not brain surgery. If I took any tactical courses, personally, it'd be with my CCW and deal with real life self defense with my CCW.
That's all JMHO, though. I don't got a lot of money for such classes. It might be fun, but I have other expensive hobbies to fund right now, LOL! I get enough bird hunting during the season and shoot a few clays for practice during the off season that I ain't too worried about shooting a person at close range.