I love this game cause it gives you a chance to dimensionalize your character.
Here's what you do - just say, "please and thank you" oh and hold open doors for people. That's it. Do this for an entire day. Be polite.
Okay so how did that feel? Did you like it? Did you feel weird? What kind of reaction did you get? Do you want to do this again tomorrow? Hmmmmm.
And the final step is apply your newly found mannered-ness to your character. Whenever there is opportunity to be polite - be polite. Does this quality fit your character? One time? Maybe two or three times? Maybe your character is polite all the time?
Remember, every character, even the darkest Vampires have something redeeming about them.