As there are many different races living in Middle Earth each has to be distinct from the other. The races have been designed so that they have a distinguishable style from each other so the viewer can look at a structure and think ‘that is Elven’ or ‘that is Dwarfish’
Concept art for Elrond, king of the elves, crests and elvish weaponry. It all has a very art nouveu style about it. Even the armor though it is more subtle. The weapons are designed with decorative hilts and more curved shapely blades . The Elves are a graceful race and I think that the floral more decorative design for them suggests their nature as a species.
This design for Elvish housing shows how based around nature they are, the trees are interwoven with the structure.
Designs for their wares are much more angular ‘as if made of cut crystal’  as they’re a mining race and most of their halls will have been carved from rock, this will have translated into their armour and weaponry as well as buildings. A lot of stuff is very Celtic in design as lots of Celtic designs are also carved into stone, or Celtic structures made from stone.
The world of men is based a lot off Viking and Norse designs, the helmets were based of excavated items in New Zealand. The city of Rohan is inspired by Norse mythology/history shown by the prominent feature of horses within emblems and throne carvings etc. Alan Lee said that characters and elements of the world of men is similar to that of Beowulf. It is thought Tolkien wrote the men into Lord of the Rings to display his want for a mythology for Britain, as there is not much.
The fact that all of the races have so much historical reference in them brings it back to the fact that Peter Jackson didn’t want the films to look like a fantasy film, he wanted to look like actual historical events so bringing real bits of history into the designs made it look more ‘real’.
Designs by Alan Lee, John Howe and Daniel Falconer.
 Lord of the Rings Extended Edition DVD Appendices