Hear Me Out
This might actually be a pretty controversial opinion on a site like this, but just hear me out.
If at all possible, I will watch the show or movie before reading the book. I know that's almost blasphemy in the larger world of reading enthusiasts, but I find the whole process way more enjoyable this way. Let me explain why:
Most people who read regularly will agree that the book is better than the show or movie at least 90% of the time. Some swear that the book is always better, and I'm not far off that. As such, if I read a book that I love and then find out that there's a movie coming out in the near future, my heart sinks. I'd love to be in this world a little more, but I know the movie is going to disappoint me. The book is always more in-depth, offering more scenes and character development. Plus, the actors never look like the characters I imagined, no matter how accurate casting is. A movie can be a beautiful love letter to the author's creation, but it never encompasses the whole worth of the art because writing is dependent on both the author's intentions and the reader's interpretations. A movie, on the other hand, is much more heavily guided by the screenwriter and director, leaving the audience little to no room for speculation. Knowing that, I very rarely feel motivated to spend my time and money attending a movie that will only leave me dissatisfied.
But consider the opposite! If you watch that movie, love it, and then find out it was based on a book, you can now dive even deeper into the world that has sucked you in. You'll learn more about your favorite characters, understand their thought processes better, and be able to refer to the scenes and faces you already have in your head from the movie. Your experience is enhanced, rather than detrimented!
Believe me, I've done it both ways. I watched the first season of The 100 on Netflix before I even knew there was a book series. Once I found out, I bought the books, blew through them in like three days, and was astounded by how different (and how much better) the books were. When the second season of the show was released, I jumped right on it, more excited than ever to see everything I had read put onto the screen in front of me. Except, after reading the books and knowing how the world should work with these characters I knew so well, seeing the seemingly random direction the plot of the show took drove me nuts. I couldn't make it through season two, and I've never gone back to the show. Which is really a shame, as I'm sure I would have loved it all if it had been finished before I picked up the books.
TL;DR: Movies make really good book trailers.