Most Helpful Guy
"What are you ready, that looks interesting?"
"Could you help me find something *insert something*?"
Is he the regular, you both are, work there? Using computers and studying or books?
It doesn't really matter you just go up and talk, say hi, bump into, ask for help, comment on similar interests.
Yourself a girl and he's a guy in a library. This is already in the bag...
You could literally just stare at him and make him talk for you -__-
... Don't actually do that it's a bit creepy.
Most Helpful Girl
Ask him about any books to recommend or try to see the book he's reading and try to ask him out and maybe to talk about the book or anything in life about each other.