Get to know her before approaching for a date.
You need to find out whether she is single.
If so then see whether she is willing to consider dating guys and if she is if you might be compatible with her dating dealbreakers.
Above all, remain polite and calm no matter what she says or does.
Word travels very fast about how a guy reacts to finding out that a girl he likes has a bf or is single but has dealbreakers that rule him out.