When you look at the list of books Tolkien has written it seems very impossible to start collecting Tolkien books. Still i know
a lot of persons who own very nice collections of Tolkien work and/or
collectables and strangely enough almost all of these collections are
In every case though, the growth of the collection goes through different phases. Most of the most fanatic Tolkien collectors start out buying all books they read from Tolkien (the hobbit, the lord of the rings, the silmarillion, etc.), even not knowing a lot about the author or without any further knowledge about other works from Tolkien.
In itself this is already a very fine collection, all Middle Earth related books, especially if also the complete history of Middle Earth is standing on your bookshelves. But when you reach this point, or even earlier, you really start wandering about Tolkien, this time as a person. It really is interesting to find out more about the man who created all of these fantastic books. In my eyes this is a logic step. Then your library grows again: Tolkien's biography, or other Middle Earth or Tolkien books (good or bad) may be bought and eagerly read.
From then on there are many roads to follow... some like the languages and make a book collection concentrated on this matter, other are more interested in the inklings and start collecting c.s.lewis, etc.
Others then again start collecting every single edition of one certain book, like the hobbit, they can lay there hands on. Some like to collect Tolkienbooks in all different knid of translations, some get into critical works on Tolkien (and there is 'really' so many books out there who have something to say on Tolkien), some go even further and really buy anything Tolkien has ever written (and i guess i am one of those)... and this might really take a life time of collecting. Good luck to you all!!