What you will need firstly is Loads of sense of humor.. If you are not that funny these learn how to be funny, but do not over do it...

What u'v got to do is smile and be friendly around her... This will attract her more towards you as you are friendly...
Make sure you look your best.. Wear cool clothes... Make sure you smell good too... (lol)
Be sure to be Yourself and do not act Fake
Hint her how much of fun V-day is... Tell her that you have got loads of goodies for V-day but you do not know whom to give it to... ;)  Just give her a hint that you have a crush on her..

Well if she starts blushing or starts digging the ground with her toes then u have got your girl... Enjoy your V-day with her and do not forget to comment.. hehe