You know the book is always better, but here is why you should watch the movie first anyway.
I'm a pretty avid reader. Being one, I must admit to having always been among the population of people who when talked to about an upcoming film or television show asked in turn, "But did you read the book?" Snobby I know, but true nonetheless. That is up until recently when I started to read "A Song of Ice and Fire," the series of novels written by George R.R. Martin and brought to life through HBO's award-winning and critically acclaimed series "Game of Thrones."
After the hotly contested final season of the show, and years of following the story season to season, I found I was hungry for more of Westeros, the show simply hadn't given me enough. My sister, a tried and true fan of ASoIaF long before it's episodic counterpart came into being was quick to suggest I read through the 5 existing novels (GRRM and ASoIaF fans alike can tell you they are eagerly awaiting Martin's end to the story in the yet-to-be-published final two installments.)
Trepidatious as I was that Martin's syntax was well outside of my wheelhouse, I cracked open the first installment, aptly named "A Game of Thrones" and devoured all 700 pages in just a few days. Shortly thereafter, while reading through "A Clash of Crowns", the next in the series, I realized something my sister had told me when I first got into reading was so true it hurt.
"The book will ruin the movie, but the movie won't ruin the book." She told me when she urged me to read Gillian Flynn's "Gone Girl" in spite of my protest that I had already seen the movie, so what was I to gain from the book?
Upon thinking about it further, I realized how right she had been all along. You see, when you read a book, your mind creates a universe shaped by your own relations to the characters and their intricacies. Furthermore, when reading books your expectations can be boundless, your imagination runs wild with details that sometimes even the magic of Hollywood can't match. The more fantastical the world your novel takes place in (ie: "Game of Thrones"), the harder it is to create a true interpretation.
Sometimes the small nuances of a character or the inner workings of their brains that we get through POV in a novel can be hard for an actor or actress to match with a look, regardless of how skilled they are.
When I read "Ready Player One" by Ernest Cline, I knew solely based on licensing that there was no way even Steven Spielberg could match the universe that lived so vividly in my imagination. I still watched the movie and while it was objectively good, I still nit-picked at minor changes to the manuscript because, to me, the book held a much greater value.
When you read the book first, no matter how true the adaptation, you will find holes and they will frustrate you. However, if you watch the movie or show first, you'll find yourself pleasantly surprised by how much more the universe expands for you when you crack open its origin.
The moral of the story here is this: the book is better, it always will be, but the movie isn't that bad if you aren't predisposed to being a snob about it.