I’d become a prima ballerina.
Singing. It brings me some of my greatest joy, and I’m barely mediocre (even with the voice lessons). I can’t even imagine how great it would make me feel if I were truly a master.
Most won’t think of this as an art, but they’ve not been to Longwood or Buchart. I’d love to be able to layout and grow an English garden, or a create a stone garden, or create a bonsai that my great-great-grandchildren can enjoy, or otherwise turn a blank plot of land into a restful and pleasing place.
Those that can, have my awe.
Well, I can sing really well. The only thing I do well enough to feel comfortable bragging about. But I wish I could play the guitar at virtuoso level.
I am a singer and a musician and am very grateful for the talents I have. But it would be so cool if I could be a stand up comedian!! I mean to be able to tell jokes in between songs or have some really funny witty comebacks or something would really be an added bonus! 
Air guitar. 
That was so funny I almost swallowed my own tongue.
Music!
Writing. I love reading, and I can write mediocre stuff, but I just can’t write something I consider good. Sniffle
Barring that, I wanna learn break-dancing. But my sense of balance is terrible (I can’t do hand- or head-stands), and I’m not limber enough. Grrrrr…