While it is possible to crack a smile when you’re in a bad mood, smiling under these circumstances can sometimes make people wary of you because they can tell the smile isn’t authentic. Offer a genuine smile to others whenever possible.  To ensure that your smile is genuine, don't smile when you just aren't feeling it. If you do, it will give others the impression that you can't be trusted. Remember how it feels when you do crack a genuine smile. Try to regain that feeling each time you smile. Even if you aren’t in the best mood, think of something that truly makes you happy before you smile. That can often lead to a genuine smile. A genuine smile comes from being happy and positive. Be happy that things are going well for the person you're talking to, that someone's joke is funny, or that you're about to eat your favorite food.  Even when you aren't feeling cheerful, you can still find reasons to smile. Focus on the positive things that are going on in your life and it will be easier to smile. When you're dealing with a person or situation that makes you feel ambivalent and you're not sure whether a smile or not, err on the side of smiling – find one thing that is positive about the person or situation and use that to create your smile. Think about someone you care about, such as the person in front of you, or something that you genuinely love to do. It's much easier to produce a natural, easy-going smile when you focus on the people or things that you love. If you find yourself in a situation where it’s important to smile and you aren’t necessarily feeling it at the moment, it helps to have a mental list of people and things that you love to run through in your head to make it easier to smile. When you’re having fun or enjoying yourself, it’s always easier to smile. See life as an adventure and allow your inner to the child to play by engaging in games, sports, and other leisure activities. When you’re playing a game or participating in an activity with friends and family, avoid getting overly competitive....

How would you rephrase that briefly using Vietnamese?
Mỉm cười một cách chân thành. Mỉm cười khi bạn cảm thấy tốt đẹp. Mỉm cười xuất phát từ tình yêu. Mỉm cười khi cảm thấy vui vẻ.