Start by cleaning the stone (if that doesn't improve the look for you then you can consider a topical application like a white wash).

http://www.todayshomeowner.com/how-to-clean-stone-around-a-fireplace/

The mantle definitely needs an upgrade and some more mass to complement the overall 'look' of the fireplace. Go with a reclaimed wood option if available.

Thank you so much. Great ideas.