I imagine you don't have the confidence to approach her in the bus, where everyone can hear you.
So, mechanically speaking, you would have to get off together with her. And then to approach. For this, you should study her that day and see her energy level - is she tired or fresh, is she lost in her thoughts or is she looking around attentively....
There are hundreds of approaches you can do. The most honest one involves your genuine smile, approaching her from the side as she is walking, and telling her "Hi..I like you, and I want to get to know you...My name is Tan (shake hands) and I have noticed you in the bus...I don't usually walk up to people out of the blue, it's just that I really wanted to meet you...you could always fall in love with a guy with a Ferrari, and then I would lose track of you" - KEEP TALKING ALL THIS TIME, it's gonna take some minutes before she becomes comfortable with your presence and eventually she starts talking and asking questions.
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