You just ask her to go out with you a place that is natural for you ie. drinks or restaurant or whatever. Be polite and respectful and don't try to be something you're not ie. speak in a certain way other than how you'd normally speak!
Best way to ask a woman out is not saying it right away, if your close to her for example work with her and see her every day, watch her (not obesessive) see what she does, what she likes, and how she communicates with others, then only you will know if shes; 1. What your afer 2. Out of your league If it seems good, and she makes the odd eye contact with you and smile, talk to her. Find out stuff about her, dont be too nosey or be too pesonal, if you feel some static between you (good static) ask her out