How to follow up with a girl?

im in a small highschool where everybody already knows everybody, so i have reputation tho im not exactly sure how it is. but when i hang out with a girl for the first time i can never become more than friends with her. like we can have a good time but then we dont really hang out again and just say hi in the hallway. what should i do to hook up with her eventually? after i spend a day with girls should i bombard them with texts and try to make plans again? should i talk to them on ichat a lot? i feel like its really hard to get a girl to want to hook up with me even if they like me as a frend. also if a girl would hook up with me how do i even get her in a situation when we can hook up?