Do what I did this year, I liked a girl named Kaya, and what I did, was befriend a semi-popular person who is brave and can talk to her, then get him/her to randomly bring you into the conversation and keep talking even when yalls covo is over, and she may end up friends with you!
well i was always the popular girl......... (lol not bragging i swear) i was just really social! so be SOCIAL! talk to her,let her borrow your clothes, invite her to your house,hang out with her! give her LOTS of compliments but limit it to where she dosen't think your a stalker or a lez.... and become friends with some of her friends and slowly climb your way to the top! try not to slip up. one thing she dosen't like and your done with! but good luck! :)
Start off with a simple introduction, like saying "Hey I'm __". Then, start a simple conversation using an average but still interesting topic like music or something like that. Continue to talk from there on and I'm sure you two will grow to become friends. Be sure not to push anything and dont act fake around her because that does NOT make people like you and you wont earn friends from it. I hope everything works out for you :)