tips on not disrespecting locals or the culture

Hi, i apologize in advance if i sound dumb. i’m going to vietnam for my 20th bday in late april-early may alone. i’m from the US and have never been outside of my country before so this will be a new experience for me. what are some good tips or things i should know? i really don’t wanna disrespect any locals but also don’t wanna get scammed. i’m staying in Old Quarter Hanoi for the beginning, then doing a 2 day 1 night cruise in the bay on an Indochina Junk boat, then going to Ninh Binh/Tam Coc. my last couple days i plan on leaving undecided and will either stay in Tam Coc or Hanoi. whatever place i enjoy more i will stay in. does Hanoi have a decent night life? i’d like to see the street train so if anyone has tips on that i’d appreciate it. do i need to consider how i dress compared to the us or some things i should avoid saying or interactions with locals to avoid? :)