Best way is just to tell her. Don't text her, not on Facebook, in person. Nicely tell her you like her and would like to get to know her better!
I've really started to like a girl (she used lots of body lauguage). But it's school vacation and we see each other only in school. I've tried some things like liking her pics on FB. She seems to be shy. How do I show her that I like her?
Don't come out and tell her as it may scare her off here but try being best friends first as the best relationships start as great friends first. By paying attention to her it will let her know you like her so find out about her likes and dislikes and find a few you two have in common and build a friendship/relationship on it. Be the perfect Gentleman and don't rush into anything so nice and slow will win here. Good luck and Merry Christmas