Always be yourself!
Keep things in perspective. Girls are human beings too! :)
No one is asking you to decide on whether to cut the red wire or the blue wire! Dating and socializing should be something fun and enjoyable.
Seriously lots of girls are just as nervous around guys they're attracted to as well. Everyone goes through some initial awkwardness when branching out in the dating and romance arena.
If you have to become someone else to attract a girl then she is not "the one" for you! You want someone to like you for who (you) are.
Just be kind and considerate to people you meet. The more laid back and casual you are the easier it is to express your "authentic self".
If there is a mutual interest in a topic of discussion or hobby that tends to help both people relax. Establish rapport and go from there.