What Kind of Formal Expressions to Greet Someone?

Hector, what should i say if i meet someone within this context? Well, you can add some formality to ou greeting by using the word mui. Em, what could i use that would eh make them think that i'm pretty conversational in spanish already? What sort of informal greeting would i need? For for more informal situations, you can just remove the second word and usus buenos or buenas depending on the time of day.