If given a choice would you read the book first or watch the film?
For those of you hopping for a clear answer to this question, I'm sorry but I'm going to disappoint you. There are some films where I only found out they were based on a book as the credits rolled, and others where I only watched the film because I'd already read the book. Strangely there have been good and bad experiences regardless of the sequence. Here are just a few examples, and the order I'd personally recommend (feel free to disagree with me in the comments).
Jurassic Park, Michael Crichton
Recommendation: Film then Book
I'm starting with Jurassic Park as it was the first time I'd really thought about the question of which to read/watch first. When I saw the film I had no idea it was based upon a book. It was only when the follow up film, The Lost World: Jurassic Park, was about to be released that one of my school friends offered to lend me the books.
Now I had really enjoyed the first film; it had a plot, it had amazing special effects, and a good musical score. The book, however, is better. There are more dinosaurs and the kids are slightly less annoying. I think I'd still have enjoyed the film had I read the book first (the special effects would have kept me interested) but I would definitely recommend seeing the film first and then allowing the extra scenes in the book to add to the experience rather than being disappointed when your favourite scene is cut from the film.
As for the follow up films; I suggest ignoring them completely. The second book, is well worth reading, but has little in common with the second film. The third film, Jurassic Park III, has little in the way of plot, although it does use some of the scenes from the first book that never made it into the film, but that isn't really enough to rescue it.
Harry Potter and the Philosopher's Stone, J. K. Rowling
Recommendation: Watch the film, don't bother with the book
While there was a lot of hype around Harry Potter, even before the first film was released, I didn't have any intention of reading the books or watching the films. I did eventually end up watching the films though, some of them even at the cinema, and I thoroughly enjoyed them. Okay, so there is some poor acting in the first film, but given many of the actors had never acted before this isn't exactly surprising, and I think adds to the charm of the early movies.
After having seen the penultimate movie, Bryony suggested I read the books so that I didn't have to wait for the last film. This seemed like a reasonable idea, so I went back and started from the first book. Unfortunately it's terrible. I know it's aimed at children, but I find it badly written and lacking in convincing descriptions of many of the key scenes or sequences. The latter books, which are aimed at slightly older children are much better. I'm guessing that just as the child actors learnt to act, J. K. Rowling learnt to write as the sequence went on. If you have already seen the films and now want to read the books, then I'd suggest skipping the first book entirely, I promise you won't be missing anything!
Tell No One, Harlan Coben
Recommendation: Book then Film
Tell No One was the first book I read by Harlan Coben. It was a gift and so I had no real expectations of what it would be like. It is, however, an excellent novel; one of those books that you find hard to put down. When I heard it was being turned into a film I could see how it could be a great movie. Then I found out that it was being filmed in French, a language I don't speak at all.
When I eventually got hold of a copy of the movie I watched it dubbed into English, rather than trying to keep up by reading subtitles. Even then it was quite difficult to follow. I think that had I not read the book I would have been unable to enjoy the film at all. It is of course difficult to criticize the movie given that native French speakers might find the experience very different, but I certainly wouldn't suggest watching it without having read the book first.
The Hunt For Red October, Tom Clancy
Recommendation: Either the book or the film first
I first saw The Hunt For Red October a long time before I read the book. Having also seen Patriot Games and Clear and Present Danger, I actually made the decision to read one of the other Tom Clancy books (from the same series) first so that I could judge the writing without knowing the plot.
Tom Clancy's novels are extremely detailed, often with an unbelievably large number of interconnected plot lines. As such the film adaptations have to leave out quite a large amount in order to keep the running time down. Fortunately, for the novels that have been filmed this doesn't really seem to have detracted from the story.
The General's Daughter, Nelson DeMille
Recommendation: Book then Film
Like the Tom Clancy novels and films it probably doesn't matter too much which way around you read/watch The General's Daughter. The film is good adaptation of the book, although it does change the settings for some scenes, and expands on some issues only briefly mentioned in the book.
My reason for suggesting you read the book first, is that I found it impossible to read the book without picturing John Travolta as the main character. Normally I can easily separate the characters from the actors that play them but for some reason with this story it was almost impossible. Not that there was anything wrong with his portrayal of the character, but when reading a book I prefer to imagine the character as described and not as depicted in a film.
So there we go, a few examples of film adaptations and which way around I think you should read/watch them. As I said at the start though there doesn't seem to be much of a pattern that I can use to predict the ordering for the future. The only common thread seems to be that if both the book and film are excellent then the ordering doesn't matter too much, but given that you can't judge either the book or film without having first read or watched them that doesn't really help!