If you are already friends and want to take things to the next level, then ignore this step. However, if you just met or are only casual acquaintances, spend time together in a group or ask her out indirectly. This might require you to have a good opener or conversation starter.  Start with a pre-opener: whenever you see her, make eye contact, smile, and say “hi”. Next, start a general conversation. Compliment her on her achievements, or ask about her interests (music, movies, books, hobbies, etc.). Use this general conversation as a starting point for developing a closer relationship based on common interests and/or shared goals.  Be patient. Some girls are naturally more open about themselves and talkative, whereas others might be more shy or hesitant at first. Never use cheesy pick-up lines. Not only does this set a bad impression, but it can also be offensive. You can be upfront and ask her out directly, or use a more indirect approach such as asking what she is doing this weekend and if she has any plans.  Which approach you choose depends on the situation and personalities. Other indirect examples include: asking whether she's been to a certain restaurant, and wondering if she wants to check it out with you; or phrase it as an opportunity, such as “we are both free this weekend and the weather looks nice, so why don't we do something together”.  Remember, at this stage you are only asking her to go on a date (to a movie, concert, dinner, etc.), not if she wants to be your girlfriend.  Make it clear you just want to hang out. Don't talk about relationships or ask her to be your girlfriend. Do not corner a girl or make her feel trapped (physically) when asking her out. She might say no because she feels uncomfortable and intimidated.  If she seems reluctant to go on a date with you, invite her to do something with a group of friends. Organize a picnic or go to a dinner and a movie with a couple friends. On your first date (or first time you hang out), your goals should be to make sure she has a good time,...

TL;DR in Vietnamese:
Tìm hiểu cô ấy trong bối cảnh thân mật. Mời cô ấy đi hẹn hò. Tạo ấn tượng tốt vào ngày hẹn hò đầu tiên.