How to approach this girl? GIRLS PLEASE.?

Im a freshman in highschool, so im not too old yet. There is this girl who has been going to the same school as me since 1st grade. Shes really hot and I really like her. I only have 2 cles with her this semester, year i think. How do I talk to her? The only time would be before/after school, but what do i say? Do i just start saying hi all of a sudden or what? Please help Girls I would like your answers. What would be too akward, what would be to subliminal?