Peter Jackson, the director of the films, used more than 150 locations around New Zealand to re-create Middle Earth. Lonely Planet has a great overview of major sites to visit: https://www.lonelyplanet.com/new-zealand/travel-tips-and-articles/77538.
The tour that most appeals to me is a 13-day excursion: http://www.discovernewzealand.com/tour-package-13-day-land-of-the-hobbit-1117. I think it would be a great way to explore the country and visit the film locations of the fantasy films.
Of course, if you don’t have the time for such a lengthy tour, it is possible to just visit the Hobbiton Movie Set, where you can take a look at Bag End, where Frodo and Bilbo’s adventures began, get lost among the hobbit holes, and visit the Green Dragon Inn, the mill, and the Party Tree (http://www.hobbitontours.com/).