I'm not talking about FAKING that you're an improved person. I'm talking about improving your REAL self, and THEN "being yourself".
For instance, if you're really fat, let's say....the admonition to "be yourself" does not mean, "Hell man, my breath doesn't smell bad to ME, so why bother flossing and brushing, I gotta be Me...and, I'm a lard-ass, so take it or leave it, sugar."
If you're so shy that you can't even look a girl in the eye when asking her out, that maxim doesn't mean, "Yeah, go ahead and never look girls in the eye, and just wait till you find a girl who gets off on guys who are too freaking timid to look them in the eye! 'Cause that's the REAL you!"
I think it's better to think of it as, "Be the real you with reagrds to your qualities", such as...there's nothing wrong with liking Depeche Mode, and hating Green Day.
So if there's a hot chick who likes Green Day, don't tell her you love 'em, 'cause it'll only put you both in Hell when 6 months down the road, she asks you to tour around watching every Green Day concert and the pressure of pretending to love it when it's really grueling for you will strain things.
It Doesn't mean, "Hey, I pick my nose, so does everyone, so, I'll be myself and casually pick my nose right in front of her on our first date. "
Be realistic.