Let’s look at races in fantasy. To my experience most stories contain about three to five different races at a whole, and there are a few of them that seem to always be there: humans, elves, and dwarves. Sometimes there are halflings as well, and on occasion dragons. I’d say these five are the “regular” races. Everyone already knows what they’re about and what their special features and talents are.
Because everyone’s already familiar with them you probably want to either stay away from them or reinvent them for your story. Of course, including the regular races would mean less work for you, since you don’t need to introduce your reader to a whole new species and their quirks. That doesn’t mean you should be lazy about them though. Be creative about how you introduce them, give them some new traits you haven’t seen before. Do something different with them this time, so the reader doesn’t get bored.
Another way to make your story more original is to make a whole new group of people. But to create new races require some more creativity and structure. You need to put down some parameters for your new race, as well as history, appearances, how they get a long with the other races, and so on. The more detailed you are in the beginning the easier it will be for you to write about them. You won’t get hung up on if the royal family is in good standing with the people, or if the government is oppressive or not, or if they take off their shoes when entering a house, and so on, if you already know your new race well enough to not be a complete tourist in their world.
Now, you don’t have to create your own race(s), but I strongly recommend you do. The fantasy genre need to evolve past Tolkien’s grasp. For example: the hostility between elves and dwarves need to die out. Pronto. It’s one of the reasons I’ve chosen not to include dwarves in my upcoming series the Taigeria Archives. I’m tired of stories where elves and dwarves don’t get along just because of their defining traits (however, it should be noted that I admit I’m a sucker for the crossing-boarders-friendship, Legolas and Gimli are my favourites after all).
The discussion about the genre itself is a whole other post (or ten), so I won’t go into it further.
My point is this: make new races, just make sure to think them through. And be creative.
Here's a short list of things you definitely need to know about your new race.
Status (are they rare or common?):
Special attributes (what's special about the race? i.e. powers, strengths, etc.):
Social hierarchy (age, physical strength, power, etc.):
(If applicable to your story) Governmental hierarchy (how are they governed? Democracy, dictatorship, monarchy, etc.):
Races they're on good terms with:
Races they're in bad/less good terms with:
Short overview of their history: