Saying “I love you” for the first time is really scary. If you’re nervous, planning what you are going to say can boost your confidence. Think about what you want her to know, then rehearse your declaration of love. Instead of just saying "I love you," consider going deeper. For example:  Give her reasons why you love her. Tell her when you fell in love with her. Let her know how special she is to you. Decide if you will keep it simple or make it a grand, romantic gesture. Telling someone you love them is a personal, special affair. You want the moment to be perfect. Pick a location that is private, perhaps even meaningful to your relationship, and a time that is appropriate.  Don't express your love for her in the middle of class. If you are with a group of people, pull her aside. You can plan a special date for the occasion. Take her on a walk or a picnic. Tell her during a dinner you prepared for her. In addition to preparing what you will say, you should also prepare for her response to those three little words. Ideally, she will say, “I love you too!” However, she may not feel the same way about you.  She might ignore your comment or divert the conversation to a new topic. If this happens, do not ask her, “well, do you love me too?” Be prepared to give her some time and space to digest what you said. Try to go on with the date as normal. Remain calm and mature if she rejects you. Have a positive, kind response prepared—your maturity just might impress her.

TL;DR in Vietnamese:
Tập nói những gì bạn sẽ nói. Chọn đúng thời điểm và địa điểm. Đừng tự cho rằng cô ấy cũng thích bạn.