If you don't already know it, find out from her family and friends what her favorite meal and dessert are. If you're both over 21, if she likes wine, get her favorite. Fix her dinner, get some candles and some romantic music she likes. Pick out a movie to snuggle up to and also if you're at the stage where you're intimate a hot bubble bath with dessert and a glass of wine/champagne can be very nice.
i cant think of any one thing, just sit back and think about her. does she want something like jewls, or a night out just the two of you and dinner. what i would like would be a nice card in the am then maybe a flower and little card sent to me at work, even if its the day before. i hope this helps some good luck