take her somewhere special to you that you normally wouldn't bring other people, if she is a good girl she will understand and love it, but if she is the type that only enjoys fine dining, then your in trouble.
Be a real man, and take her to your house, and make her a dinner you know she will like (plus, dessert). Then, get some popcorn and watch a movie. Don't forget to give her flowers. It will just be the two of you, so let her know not to worry too much about what she's wearing (assure her she looks beautiful no matter what).
Or, you could take her out to dinner at a fancy restaurant, like any other guy would.
this is vatoloco a really great romantic date would be take her to a Mexican restaurant where you now theres going to be mariachis music and try to learn a Spanish song you could sing to her memorize it practice it and sing it to her with live mariachi music believe me ive tried it and girls go crazy for it and start crying if you play your cards right tip a 20 to the mariachi musicians and let them know you want to sing a song to your girlfiend in Spanish and then they will follow you to the table and play the tune for you don't be shy you can have a couple of margaritas sow you will be in the mood and wont be that nervous believe me your gonna have that girl sweating in the palms of your hand go for it good luck your friend vatoloco crazyman.