Watch the extended editions.
And if you've already done that, watch the Hobbit movies and the extended editions of those (have to wait a little bit for the extended edition of BotFA though). Then once you finish that, if you're really ambitious, you could watch all of the above with director's commentary.
Oh ya, read the books as well, it's worth it. Start with the Hobbit, then read the LotR trilogy. Then, even though it takes place a long time before, read The Silmarillion after that because, despite being a prequel, I found it worked better when I read it after because it ties up some loose ends and explains schtuffz. Then, if you're still bored, move onto Unfinished Tales, and your journey through Middle Earth will be almost over.
Then do it all again.
Don't forget The Children of Húrin.
And if you are REALLY ambitious, the 12 volume History of Middle Earth.