That's pretty common in comics now anyway, it's lame but hell most major publishers have artists who base characters off actors. Many a time Norman Osborne has been Tommy Lee Jones, and the Wanted comic pretty much starts Eminem.
As for improvement, unless it's a drastic change in style 9 times out of 10 it's going to be subtle and gradual over the course of a lot of work. It also comes with trying new things with your style, and unfortunately that's hard for any working artist since fans are pretty stubborn when it comes to change.