Unfortunately, there isn't really a Mafia University for you to attend. This is an unusual occupation (putting it lightly), and the training you need to be successful is also unusual. While you don't need any fancy expensive degree or formal education—or even a high school diploma—having some semblance of intelligence or skill in the following areas is necessary to put on those silky Don pants:
Leadership and organization skills—when you tell people to do something, they'd better do it, or else the whole organization crumbles and you have to make an example out of them.
Money-managing—you should be able to sniff a bundle of cash and tell if the guy's trying to short you.
Intimidation—one look from you should be all the words anyone needs.
Know your business—from gambling to bootlegging to embezzlement to construction, you've got to understand the principles in order to maximize your undeclared profits.
A cultivated swagger—this'll come on its own.
Also, it'd be nice for you to have at least a passing understanding of social media. This is the 21st century, and the modern mob boss needs to know how to stay relevant in a changing digital landscape.