I kicked off my career with a 4 week mostly practical course which was from the Armed Forces resettlement. I soon learned that this may have been a good starting point but was certainly not all I needed to know.
It was good enough for me to do small jobs alongside another job until I fell into something else. I have recently started this sideline again with the view to changing over at some point in the future but there is still tons I need to know.
Unfortunately not everyone can do years in a college to learn their method of earning a living or go back in time. There is no quick fix way to become a Plumber and as was said it depends on what you call successful, to me being this would be earning enough money, have a full order book, have people call you back, having their friends/family call you in and not having to return to fix it! Aslo to reach the stage where you wouldn't need to advertise too much.