How can i get this girl to like me?

Basically, i like this girl, and we flirt a bit and talk a bit and i can make her laugh alot. without sounding big headed i'm pretty sure she is on the verge of liking me, cause i get these hints, but they never follow up with the obvious hints that a girl likes you, such as watching you when you walk away. i'm still in school (sixth form) and she's in 2 of my classes and i want to know if there's any advice people can give me to make her like me apart from just telling me, 'talk with her' and so on...