I would start off with the Silmarillion or the Hobbit. Don't read it too fast, but don't read it too slowly either. Or read it two times, or even three. Yes, that will do. Or more.. Decide yourself. I would recommend you to read it at least more than once.
Then, go ahead and read the Unfinished Tales and the History of Middle-earth series. Now, I'm sure you will know a lot more after that. Really, a lot.
Oh, and if you can find time after that, and still are fine with the works of Tolkien, read the Letters by J.R.R. Tolkien.
Well, I think that will do, for at least quite some time. Good luck, laddie.