OK, here's the classic look for girls: pink tights, pink shoes (preferably canvas), solid-colored ballet-cut leotard over it (long sleeve, short sleeve or tank/camisole is OK, get whatever style of BALLET leotard fits your fancy).  Wear a ballet skirt if you would like a little bit more cover.  Wear legwarmers if your legs are cold.  Put your hair in a bun.  Don't wear panties under the leotard, panties sticking out under your leotard and showing through your tights are NOT a nice sight.  Don't ask me the details of how it all works with feminine hygine, etc.  Don't wear pantyhose or L'eggs, use real dance tights.

When my beginner students come dressed in the classic look, I know they are serious and ready to learn!  When they come with layers upon layers of stuff, I can see that they don't feel confident about their bodies and they're going to be timid.