How do i talk to her if she likes me and i like her too?

I like this girl and im pretty sure she likes me too. like she looks me in the eyes all the time from far away. And she looks at me when im in a group of people and then she puts her head down. I think she likes me and i dont want her to lose interest in me so how can i talk to her in a friendly way at first. Would i just go up to her and say hi? If she likes me she wont call me out on it in a mean way? What should i say and how should i say it. I see her before homeroom and between 3 and 4 period. right before lunch when she is at her locker seems best because she is normally with her friends other than when she is walking to cl. i have her in gym too i see her before and after gym starts and ends. she is normally with atleast one friend all the time other than before lunch and sometimes between cles.how can i approach her and what should i say?