When i was in high school I was not good at all in figuring out when girls are flirting. cus I always tell myself not to assume anything.
I'm that same type of guy. I can never see all the social cues of when a girl is coming on to me, until my friends tell me what's going on. What works for some is just simple, straight language — forgo "batting your eyes" and all that. Just ask to hang out with him and take it slow from there. Build up a rapport to ease the friendship into something more intense.