My brief relationship with a girl from Japan ended badly, partly because I suffered from niceguy-itis, I think.

Not sure I can offer much advice. I wouldn't reccommend changing your behavior too much, unless you'd want to change it even aside from trying to make a good impression. Any permanant characteristics (like your niceness) are likely to come out eventually anyway, best for her to figure out if she likes you know than get to like a you that doesn't reeally exist.

That said, it's easy to make mistakes in the name of being nice or a good host. I ruined things with that girl by coming on too strongly, and way overdoing my first Valentine's Gift for her. I can only imagine how creepy it seemed.

Then again, I overdid my first Valentine's Day gift to the next girl I dated as well, and now we're married!