The biggest thing is not to get hung up on one girl. In fact you can use this girl as a pawn or as we say in the game "social proofing". If other girls see you talking to you and your friends they will see you as a male who has been "pre-selected". All the usual
PUA jargon but it works.
But If you really are hung up on this girl and you'd like to give it a go you have to recognise you are in the "friendship zone". Cut yourself off from her for a while so the next time you see here the relationship has changed a little through time. If comes up and flings her arms around you you have to make a comment like "hey hands off!..girls have to EARN hugs from me!" (playfuly of course). Do not jump through these hoops for women!
You will then need to throw a few playful negs at her and get her to DHV you. All the time she is having an interesting conversation with you you need to act like you're about to go by saying "I better get back to my friends but"
And lastly if she asks you to text / call her say "I'm a little busy all this week I can call you on saturday evening if you like? If she ignores the call leave a message saying "hey you asked me to call you but I guess you're out and about" I'm not going to be around for the rest of the day so maybe I'll catch up with you another time" If she listens to the message and wants to talk to you, don's worry, she'll soon call straight back.
Lastly ALWAYS END THE CALL FIRST!!!!!!!! preferably when the conversation is good. Your excuse should be.. I'm meeting one of my friends for lunch/dinner.. "SHE's having a few probs with her boyfriend and wants a good night out to cheer her up"
See how it goes fella. But as I said at the start. I would move on to pastures new, she'll soon get jealous if she sees you with a few other girls.