It depends. If the books were really popular, I have most likely read the books first. If a movie was made based on relatively unknown books, then I would ask about books. But for me, I usually read the books first :)
I usually read the books first but there's also times when I didn't realise the movie was based on a book so I went and got it afterwards. But the books usually make the movies look terrible because they take so much out :P
I usually try my best to read the books first, but it doesn't always happen. Some notable exceptions are: Twilight (I wasn't planning on reading or watching it though, so it's a special case), Marley and Me, and Pay It Forward. There are others, but I'm too lazy to try and remember them right now.
I don't. Except for my favorite, and second to only favorite book, skulduggery pleasant. Wich will be in theaters probablly next year and the book " the outsiders" wich I read in school and saw the movie in school.