How to approach girl on train?


I saw this cute girl on the train. I wanted to approach her but I had no idea what to say. How could I have done it without being creepy?
Can you give me some context? Like where were you going? Is this a train ride you always take? Do you see her often on the train? The best approach is tailored to the context.
Well, I was hoping for an all kind of situation where it doesn't matter if I've seen her 100 times or only once. Also, if I had seen her several times, I'd probably be able to work some kind of angle over a few rides, this is more for "could be anyone" and never seen her before/likely not to see her again. Thanks!
Someone pretty incompetent at dating here, but I can give you the non-dating kind of way to talk to people on the train (in Germany which might be different, but in general people here don't talk that much on the train either). When I take a seat I may make a comment if is something interesting about the other person(s), like the have a funny packet (one time there was a huge vacuum cleaner box and I asked whether she could recommend it). But starting a conversation *after* waiting some time would be creepy.