This might also fit into "world-building" but I think it is a matter of writing.
I'm reading "Mistborn" by Brandon Sanderson at the moment and all in all, I really like his magic system. But there's one problem. During the fight scenes I still have no real concept as to what the characters can do, what happens when they do and so on. I'm sure Sanderson explains it somewhere before but it still takes going back and rereading to really understand which makes following the fight scenes rather hard. And he's already being critisised for spending too much time explaining his magic system... (I don't think so, but I really like to read explanations for magic systems or I wouldn't be hanging around forums like this.
Writers dealing with fire balls, elves and vampires do not have this problem, these concepts already are familiar enough for everyone to have a clear picture in their mind but with the more original concepts we all like to see this becomes relevant.
If you're using fantastical elements which aren't familiar to the general public, how do you make these come alive? How do you allow the reader to come into the character's head and allow him to feel what the character is feeling?