I've done a little bit of this at a class at BYU. Basically I sucked the first time I carved out of wax and wax-ups were even harder because the wax melts so fast. We didn't get too much practice, but it's one of those things that I was terrible at the first time, then really bad, then bad, and finally had a clue as to what was going on.
I am not artistic at all, but you learn to see things and understand how they work on the tooth (maybe some PAT skills coming into play). Then you start to understand how to recreate these things with your instruments. It can be fairly mechanical, but our instructor said you can be mechanical (not artistic) and still be very good. I imagine however, over time a little artistic flair creeps in and you start appreciating the beauty of good work and things become more natural and organic and less analytical.