Think of all the times you were like whoa, that girl is so hot. You were eager to hang out. You called/texted them all the time and got upset if she didn't reply. If you did get a chance to hang out you did all you could to impress her. That all comes from a place of scarcity meaning you think she's the only girl out there for you.

What you must do is the total opposite. Don't take too much interest, if you don't have time to hang out don't change it all for her, less texting, less calling, you get the picture.

What this does is it puts you in the driver's seat. Girls are used to having guys practically on their knees begging to be theirs. She'll take notice that you aren't like the rest and that will draw more interest in you. Is it guaranteed to work? No but its better to be the one scarce instead of the other way around. Trust me it feels so much better when you don't need someone im your life.