Fantasy worlds, for many people, are brilliant things. In a book, you can dictate almost all of what happens in this world, populate it with whatever you like and so on. The main problem though, is being careful with how much information you unload on your reader.
There are lots of things to consider:
- The Arcane
- How much the reader knows
- Where you begin
- Why your character's story is important
And so on! It's a fantastically fun thing to do though, so don't let this discourage you from creating your own world. Think about it - you can dictate EVERYTHING that happens, unlike a detective story in this age where you have to be realistic and can't make everybody have a superpower unless connected to some secret organisation where DNA is changed in bodies of the newborn, etc etc. In fantasy, you don't have to have an excuse for everything. You can just make it be so.
Let the discussion commence!