So many people think that if you're writing fantasy, it means you can just make everything up as you go. Want to add a dragon? Add a dragon! Want some magic? Throw it in. But the thing is, regardless of whether you're dealing with realism or fantasy, every world has rules. Make sure to establish a natural order.
It's always hard, when introducing readers to a new world/set of rules, not to lay it all out manual-style in the opening chapters but make sure to put the action and the characters at the front. If people don't become invested in them and in the story, the world in which it's set will become a burden.