You can paint it, add or replace the mantel... here are some more ideas for you:
Some great 'whitewash' updates out there for fireplaces
You can paint it, tile it, add marble or granite to face and a new mantle.
We used pallets. :http://alifeunfolding.com/blog-1/2016/10/6/rental-housequick-and-easy-fireplace-update?rq=Fireplace
Please post a picture of your fireplace. Once we see what you have to with, we can then offer suggestions on how you could make improvements.