Smiling is a powerful way to boost your mood and makes you appear more friendly and attractive. Even the action of smiling can relax your body and improve your outlook. When you’re feeling nervous around your crush, give them a confident smile.  This doesn't mean that you have to smile 100% of the time like a Barbie doll. Instead, flash them a quick smile to show that you are comfortable around them. Try to smile with your eyes as well; this will make your expression look more natural.

How would you rephrase that briefly using Vietnamese?
Mỉm cười để trông có vẻ tự tin và cảm thấy tự tin.