The higher up in the levels you go, the more important grooming seems to be. What I mean is, if you're new and are dancing at a lower level, then the judges cut you a lot more slack than if you are dancing at a higher level.
I have a tape where about a dozen judges talk about what they look for when they judge. And every single one of them brought up "grooming."
The most important thing is to make the most of who you are and what you have. Don't be down on yourself for not being a size two, but rather make sure that you gown fits properly and is flattering to your age, shape, coloring, and the way you dance. Make sure you wear the right kind of shoes (satin, dyed to match your leg color, and clean), have your hair done with no flappy bits, and wear sufficiently applied makeup (most newcomers wear far too little).