In J.R.R. Tolkien's fictional universe of Arda, Middle-earth, also known as Arda, is in fact Europe. The entire landscape resembles Great Britain, France, Spain, Russia, and Italy. Roughly positioned, the Shire and Imladris are positioned at about the latitude of Oxford, England, Great Britain. Therefore the Old Forest and Bree are positioned roughly about the south-east of England, possibly Norfolk, although this is unconfirmed. Rohan is apparently the name of a famous political family in France, although Tolkien also apparently did this unintentionally.
Moving down south, we find that Helm's Deep is possibly also either in France, Spain or northern Africa, and therefore so Gondor is roughly at the latitude of contemporary Italy. This corresponds neatly with history because Gondor and Italy both involve politics and civilization, and also seemed far more civilized to the rest of the world at large, what with Rome being at Italy's center. Therefore, moving east, we discover that Minas Morgul is around the border of France and Italy, and the Black Land itself is positioned right in the center of the Black Sea. This is likely no coincidence, because Black Sea in Elvish would be Morgaer.
Moving much further south, we discover that Khand and Harad are more likely positioned in Africa. Khand itself is possibly the great deserts of Africa, which were both unknown to the "civilized" inhabitants of planet Earth because of their remoteness and apparent lack of civilization. However, as shown in both The Lord of the Rings: The Return of the King and past history, tribes were discovered to reside in Africa and Khand, but were assumed to be barbarians, because they formed their own civilizations and stuck away from western society. Rhûn is probably positioned in Russia or another countries of the east of Europe. This is very probably since Mordor is ubicated in the modern Black Sea as stated above and Rhûn is on the north of it.