The Mob in Books, Film and Television
Study novels such as Mario Puzo's "The Godfather" and Peter Mass' "Serpico," movies such as "Once Upon a Time in America" and "The Road to Perdition," and TV series such as "The Untouchables," "Mobsters," and "The Sopranos." These will give you a feel for the historical, cultural and sociological context of why and how mobsters operate within their organizations and community. "The Mafia Manager: A Guide to the Corporate Machiavelli," an insider view by the anonymous "V," explains the hierarchical operations of managing friends and enemies, staying cognizant of potential threats and rewarding loyalty. All of these are crucial elements to weaving an authentic mob genre story.
Nonfiction vs. Fiction
Determine whether your mob genre story will be based on real gangsters such as Al Capone and Bugsy Siegel or whether it will be a fictionalized tableau such as "Boardwalk Empire," which uses the historical backdrop of Prohibition-era crime, prostitution and bootlegging. Although fiction gives you more latitude in storytelling, accuracy is still critical in describing locations and clothing as well as emulating mobster slang and depicting legal and judicial proceedings. Since underworld crime exists worldwide, also consider locales outside of the U.S., such as Mexico, Central and South America, China and Russia.
Heroes and Villains
Identify who will be the protagonist and antagonist in your story and establish credible motivations, backstories and value systems that respectively make them good or bad. Consider making your lead character a woman. Giovanni Fiandaca's "Women and the Mafia: Female Roles in Organized Crime Structures" illustrates how women are as effective in leadership roles as they are in auxiliary positions within the mob world. Introduce twists in which the mobster is more likable than the cop doggedly pursuing him. Borrow a page from Shakespeare and introduce characters that aren't everything they seem on the surface.
Conflict and Consequences
Develop a sustainable conflict. Both the protagonist and the antagonist must have something at stake for which they will take whatever risk is presented. For example, the mob character is honor-bound to avenge a death while the cop is desperate for a promotion that can only be achieved by bringing the mob character down. Ideally the protagonist should have an Achilles heel. This is often a loved one, an example of this being Sullivan's young son, Michael," in "The Road to Perdition." While it's permissible to have subplots in a mob genre story, their existence should be to either add complications to the core conflict or to help resolve it by the story's end.