How to do I get to know my crush??

How do I talk to him?? And also flirt?? I'm a social outcast in highschool and he's on varsity (everything literally).. But I've taken in interest in him and he's been a bit friendly to me as well... I don't have any classes with him so I can't really find a chance to talk with him... My next door neighbor (he's five) though is friends with his nephew (who's five) so I think I've found my way in... But still how do I talk to him?? And flirt??? What are some funny/flirty lines??