-View the movie first and then read the book
-Read the book first and then watch the movie

Both options have their pros and cons, it actually depends on each person and other factors.

My personal experience with The Godfather was to read the book first and as soon as possible, watch the film, the book and the film are extraordinary works and the best simile to describe what I experienced, is the following:

" Watching the movie The Godfather after reading the book is like having sex with someone falling in love first"

In the book you fall into the plot, you can explore your own imagination with fantastic stories of characters alive, interesting and full of mystery, for me, the book at any time was boring. The most important thing about the book is that you managed to get into the mind of the main character Don Vito Corleone, the writers know that the best characters are gray, that is, neither very good nor very bad, because both cases are also repudiated by the spectators, they aren't people with whom we feel identified; Don Corleone is one of the best constructions of a gray character, I felt a very strong connection with him, thanks to the spectacular performance of Marlon Brando, makes you think that you have been brutally crushed with a much better representation of what you could imagine while you were reading the book.