You can't by class, you are simply born with it. Being classy to me is being polite, respectful, articulate and able to be yourself in any situation. It's knowing that sometimes its best to just walk away from an argument or person because you know they are just trying to take away your self respect and have you loose your class. Once it's gone it's gone for good, you can't get back class. Being fabulous is just being true to yourself and dressing with what's best for your body type.
people think being classy and fabulus physically these days is everything but honestly they should be polite, caring, compassionate, and respect as they said below, of course most severly lack all of this as they focus too much on the physical aspects. I think being yourself is the most important thing not doing what everyone tells you to dress like, act like and look like, most guys are not my type these days because they don't act themselves, they are always comparing themselves to other guys trying to look all ripped and macho, it really is the biggest turn off ever, I go for guys who don't do all that and have their own mind, nothing beats that ever.
Being classy is a demeanor, it's the way you carry and present yourself. Having respect for yourself and others, having values (things you believe and stand firm for). Classy women do not do any and everything, they have standards. It's not about what you wear, unless you just want to LOOK classy.