How could i talk to this one girl

there is this one girl in my school who yesterday I talked to her at lunch and it was kind of a awkward conversation because I asked how are you once and after she said good and asked me how i was i said good and asked "how are you" again Now the tricky thing is that I have the chance to talk to her before school, during lunch, during study hall in the library, and even after school. Although the thing is during lunch and study hall she is with her friends and my friends told me it would be creepy if i talked to her by stopping her in the hall before or after school. The reason is because we are not friends. Now I want to know how to talk to her without seeming like a creep and what i could possibly say to her when i talk to her. And one more thing is it necessarily be bad if i didn't talk to her the day after i first day i introduced myself to her?

trying to figure out the "how are you" awkwardness. Did she say "how are you?" and you replied "How are you?" Or did you ask the question twice because she ignored it the first time?

Anyway, find out what she's into and talk to her about that. Is she a bookish girl who may share her discussions about schoolwork with you? (OMG, how did you go with that English assignment?) Is she a sporting type? (You've got that meet coming up soon?). Indie chick who likes music (are you going to that upcoming concert of X?) Is she into any fandoms (have you seen the latest Dr Who yet?) Follow my drift?

Edited to add: The thing you talk to her about - try and find a mutual interest. That way you can ensure the conversation can continue for a bit. Nothing worse than raising a conversation and then looking like a dufus because you don't know much about it. I tried that when making small talk with an acquaintance who's into politics when we were at a party once. Sadly, he does satire of politics as a living and I know nothing much about it - so I just looked dumb.

Your friends are creeps man. You can talk to her whenever you want. Shes just a human and once you see her go talk with her. Wait 0 seconds cause hesitanting will make you lose moment and spontaneous energy. Also negative doubtfull thoughts starts to creep in when hesitating. The creepiest thing you can do is look at her when you see her and dont talk. Even more creep is sit/stand next to her and be quiet. Dont pressure yourslef into half an hour talks. You should talk to her because you want to. The reason is have fun and say everything that you wana say.

Maybe at first you should work it out so that you can walk with her before and after school to where she is going. Maybe you have to go see a teacher in the same direction she is going or you have to see a friend there. Then you can talk to her as you walk about anything you think she and you will be interested in. Make a joke or ask her what's up! Then when you guys get closer after talking, it'll be more normal for you to talk to her when you see her at lunch or in study hall with friends. You'll be close enough to not feel like a creep. Just try to find a good reason to talk to her.

Does it matter if its been 1 school day but technically 3 days of the week if i last talk to her because i talked to her on Thursday

How well do you know her? Because its okay if you don't talk to someone every single day. You can still be close.

I have only talked to her once and that's it

Well if you want to show that you are interested in dating her, I would suggest going up to her and talking and flirting instead of just creepily starting at her.