Hi,
When you first meet someone, say "Xin chào" (Hello). But that word is quite general and VNese don't use it much.
They use "Chào [...]" (Hi [...]) instead.
In the [...] you should put in appropriate pronouns like:
"Bạn" (friend) : used for someone who is around your age.
"Anh" (brother) : older than you.
"Chị" (sister) : female, older than you
"Em" (little brother, little sister) : younger than you
"Chú" (uncle) : middle-aged man
"Cô" (aunt) : middle-aged woman
=> "Chào Anh", etc
After that, say "Rất vui được gặp [...]" (Nice to meet [you])
Again, please use the correct pronouns.