Fan art is a good way to get the skills you have noticed. Number one, its a recognisable face, so people know immediately if you can render a good likeness. Number Two, once its uploaded it goes into Google and anyone searching for your subjects name, will see your image if its a good one. Number Three, celebrities love fan art. I have had praise tweeted to me from the likes of Oscar winner Minnie Driver, Frasier star Peri Gilpin and Bafta winner Lauren Socha, all of which helps to get my art noticed.
Hope this helps.