If you want to be a supportive friend, one of the most important things you can do is to be happy for your friend's accomplishments. Work on being your friend's biggest fan. Applaud his or her achievements and try not to feel jealous.  Jealousy can often make it difficult to celebrate another person's success, even someone you consider a friend. However, it's very important that you are able to cheer you friend on. People want to be around positive people who make them feel good about themselves. Even if you're feeling a twang of envy, try to push past that feeling and offer a sincere, "Congratulations." You'll feel better if you do. You'll find it's much less exhausting to be happy for another person than harboring jealousy. Do not just congratulate your friend on big achievements or milestones. You should also compliment your friend on small things he or she does that you appreciate. Remind your friend of his or her good qualities. For example, say something like, "I love how you're always smiling" or "I appreciate how you always remember everyone's birthday." Listening is the foundation of a quality friendship. If you know your friend is having a bad day, offer to let your friend vent to you. You do not have to offer solutions or even advice. Simply allow your friend to express his or her feelings without judgment.  If you're unsure what to say when listening, try active listening. This will allow your friend to feel more open expressing his or herself to you. You can reiterate what your friend says after he or she finishes talking, encouraging your friend to elaborate if necessary. For example, say something like, "You feel really stressed about the way your brother behaved when he came to visit?" Keep in mind that, while listening is important, you do not want to end up in a one-sided friendship. If you feel like your friend is always asking you to listen, but is never there for you in return, you may want to reevaluate the friendship. Being a nice friend is important, but you do not want to end up in a...

TL;DR in Vietnamese:
Vui mừng trước thành tựu của người bạn đó. Lắng nghe bạn của bạn khi họ cần. Ghi nhớ sự kiện quan trọng. Sở hữu lòng trung thành. Luyện tập Quy tắc Vàng.