Ya well the library is a bit harder I think because girls in the library are usually studying (well in college they are i dont know about high school) so at times they can just get frustrated. I only approach in the library if i get an IOI or they look bored. And in they library heres a given, girls will tend to choose a spot were they are surrounded by empty seats (unless they choose a spot right next to you when there are other seat options, i would take that as an IOI) heres what i have used before to open.
HB 7:(walks to a spot surrounded by 2 empty seats)
Nick:(sitting 2 seats away)What do I have AIDS or somthing?
HB 7:No. haha

(and comes and sits right next to me)
but thats just me maybe someone more experienced can shed some light.