I have actually been advised at once to not pay too close attention class and alignment help files.
When it comes to roleplaying, there are two sides: your actions and other people's perceptions.
There is a character in game whose description shows him being disfigured, and yet, he is by far one of the most charistmatic people. I always love being around him.
Your character may decide to hold back or hide certain attributes. Such as she may be very charismatic, but due to feeling like a social outcast, she rarely has much to say.
Charisma is merely how easily you speak and work the crowds. Hitler (ack!) was a great example of how fugly and bad message are ignored when one knows how to speak to people.
But the flip side is perception, how people will perceive you. If you play a giant, they expect you to be dumb. If you play a barbarian, they expect you to be dumb. You play a paladin, they are looking for the stick that is stuck up your... You get the point.
The best thing I can recommend is this: Treat your character as a person. Her stats will play into who she is, but her/his current lifetime experiences will affect how they act. Allow the experiences they have to change or strengthen their views. Give them a personality and a life. Others will try to 'suggest' how your character should act, but this is your little life form, you treat it how you think it should act (obviously, as noted, keeping it within the alignment restrictions as Zynor said).
Good luck with your character and remember, she is yours and supposed to be fun!!!!