I'm a guy so I don't know if girls appreciate this but...I think the best way to do it is to explain to her about how she makes you feel. Don't get carried away though, like Hiroko said be to the point. Once you start talking everything will become easier, and if you think about it you will have a hard time thinking how to bring it up, so don't think about it just blurt it out, then explain yourself.
amirightladies?