The fine line – keep it a secret
This world is pretty much the way it is now, earth’s history is the same. No vampires showing up to kill Hitler or saving the queen from evil witches. Here your heroine/hero will either already be a part of this special world or find him/her self drawn into for some reason. She/he will have to keep it a secret and that in itself can make for a whole book if you want to. This way the person suddenly included in this new world will feel special because it’s such and exclusive world. This is quite popular in YA books as being special and finding “different” people you can fit in with is a big par t of growing up.
“Look a flying elephant – I haven’t seen one of those in ages”
Maybe having werewolves, fight in world war II made everyone love them? Or a super smart vampire coming up with a cure for cancer? Somehow they just came out of hiding because frankly there was no reason stay hidden – not with all the (human) rights people have now days. They would simply have to be extended to vampires and elves too, because just killing a whole race because they’re different wouldn’t go over to well with the civil rights, right?
There are some things to think about when you make supernaturals a part of the world. When did they “come out”? Why did they do it? What was most human’s reaction? How long have they been accepted (or outcasts)? Is there schools for magic? Or special werewolves camps?
The good thing about having a universe where everyone accepts that magic, vampires and other supernatural stuff exists is that there is a lot more room for action. If your hero works for the werewolf police, the chances of writing a successful fantasy crime mystery will increase. If he was just a werewolf accidentally stumbling upon a dead werewolf and he was one of the few that new about them, things might be trickery – it’s not like he could just walk up to the nearest cop and ask them to get him an ID for the wolf. There would be a lot more investigation and boring stuff before there was actually any action. Sure you can work around it but an earth with were-police might be really fun to read about and will give your story a interesting twist.
But it all depends on where you want your story to go. Harry Potter would hardly have been a success without Hogwarts castle now would it? Sometimes a change in earth’s history is necessary for your story to work.
Writing Fantasy 