I'm going to Cambodia for one month in November and I've never been outside of the US. What should I know?

I'm 18. My grandparents are going to Cambodia to visit family and I finally have the opportunity to come along, and I feel incredibly unprepared. I have 7-ish months to equip myself! I want to experience as much as possible and I have the ability to engage in non-tourist activities (my extended family has relatives close to my age.) I'm a girl, can speak Khmer well enough to navigate, small talk, and order food. Anything I should know about southeast Asian culture? I'm sadly not well versed in daily life over there, as my parents are so Americanized.