I have used various elements in analyzing Mario Puzo's writing style and here is where I shall share what I have found.

Narrative voice:  The narrative voice used is 3rd-person. The story is always told by someone outside the novel. Whether the main character happens to be Johnny Fontane, the Godfathers son, at the time or the Godfather himself. On pg.183 "He greeted Johnny Fontane with a surprised cry of delight." 

Descriptions: His descriptions are in the middle of flowery and minimal. pg.183 "Actually though it was McElroy's house party the idea had come from the practical brain of Jack Woltz himself."
Use of Dialogue:   pg.182 "I'm always charming," he said.

Literary Techniques: Imagery pg.110 "Sollozzo and Tattaglia let his hands go and only the strangler stayed with the victim, sinking to his knees to follow Luca's body, drawing the cord so tight that it cut into the flesh of his neck and disappeared. Luca's eyes bulged out of his head as if in the utmost surprise and this surprise was the only humanity remaining on him."

Genre: Realistic Fiction pg.43 "Because of the gas rationing still in effect, there was little traffic on the Belt Parkway to Manhattan."

Theme: Loyalty to you friends and family is one of the most important things in life.