Read the book before the movie?

If I got a pound for every time someone told me to read the book before watching the movie, I'd be super rich by now.

You've all probably heard of 'The Fault in Our Stars', if not seen it or read it and I've heard so many people raving about it that I really want to go see it. I made plans to see it with my sisters this Saturday but then I accidently let slip that I hadn't read the book yet and then get this, my sisters banned me from watching it until I'd read the book!

The film poster for the book by John Green

I personally don't see what all the commotion is about because, with some films, I feel like reading the book before watching the movie would ruin it for me. For example :- The Mortal Instruments City of Bones. I went and saw the movie and absolutey loved it which encouraged me to read the books. Once I'd finished all the books, I watched the film again and realised how cronic it really was. If you ask me, I feel like I did it the right way round because if I had read the books before, I wouldn't have enjoyed the film and if I hadn't watched the film I wouldn't have read the books.

People say that you ruin the storyline for yourself if you watch the movie first but I don't think that's true. I didn't read any of the Harry Potter books before watching the movies bar 'The Deathly Hallows' and I think that it actually ruined the last film for me because I had all these expectations of what it should be like and I was very aware when they missed a detail or a character. However, saying that, I don't feel like watching the movies ruined the books for me because it was almost a whole different story reading the books because there were all these extra details and mini stories that weren't included in the films that suprised me and made me even more interested in the story.

So what do you think? Should I read The Fault in Our Stars before watching the movie? Will I ruin it for myself? I don't know!!!! Help me!