Chronological order,but forget the Prequels which are nothing but a money scam,and they "REEK"!
My daughter in another state and I read the entire 12-volume set together,borrowing the books from the library. After being very 'antsy' after reading the first book and not having any others to begin,we put reserves on the rest, 3 books at a time!
I would not advise reading them back-to-back without a break as we did,however, unless you don't mind very strange dreams(me) or even nightmares(my daughter),LOL!
Loved the books,can't stand the horrible movies.