Here is how it will happen:
You will have been flirting with her for a little while - maybe since the first day of school, when you saw her and smiled a little bit because you liked her hair, you liked her shirt, you liked the way she slipped a pen into her back pocket like it belonged there - and after a few months you are friends but on this day something changes for you and her, and it starts with a note that you scribble on the back of the business card you took from the Chipotle just off-campus, which says, in your semi-legible handwriting, What are you thinking about?
You are asking only because today she seems a little distracted and so you slide the note on her desk when the professor's back is turned so he can write on the board (integration of inverse trigonometric functions) and she looks at you and you wink and she reads the note and scribbles under it, nothing, which you were very much hoping she would not write because nothing is nothing; nothing means nothing; nothing will forever and always be good for abso-freaking-lutely nothing but this time nothing is not good enough for you. You demand more.
So you scribble back, no, really, which means very little by itself but in context it means everything, in context it means I am your friend and I have been your friend since the first day when I liked how you slipped that pen into your back pocket like it belonged there and I want to know what you were thinking about and I will not accept nothing, and she gets what you are saying and so this time she thinks about it a little longer.
You have almost forgotten about the note when she puts it on your desk a few minutes later, and when you look up her cheeks are red and her eyes will not meet yours and so you open the note and there it is: I was thinking about kissing you.
You stop breathing, momentarily.
The professor says class is over and she gets up like her seat is on fire and makes a run for the exit but you are pretty quick (and you only knock over one desk it falls with a bang don't stop to pick it up that part is imperative) so you leave your bag at your desk and you catch her arm in the hallway and she turns and tilts her head up because you are taller than her and she goes to give you an excuse she goes to apologize but you do not want an apology what you want is to explain that the reason you smiled at her on the first day of class was because you liked the way her pen fit in her back pocket like it belonged there and every day since you smiled at her because you were thinking about kissing her but for god's sake don't tell her that or at least don't tell her that right now because what you do right now is ten times better than that what you do right now she has been dreaming about what you do right now is you take her and you kiss her, once, for a long time.
After that you should probably go pick up the desk you knocked over, and then maybe ask her if she wants to get dinner or something.