My personal rule of thumb is, when I discover this thing I want to watch is based on a book, I have better luck in enjoying both versions of the story if I see the movie/series first and then go back to the book. Because I can't think of anything besides The Witches of Eastwick that I hated the book for after having seen the movie, but definitely I could be listing lots of movies that were wrecked for me or others by being familiar with the book versions first.

On Dexter, I saw the whole of the first season and then found the two books at the library. And the season covered the first book, so now I'm maybe spoiled for the new season, but. Given the differences between the first book and season, I'm thinking I'll be able to separate the two versions in my head easily enough.