HEYGOW

你好 is the greeting every course opens with, and the one native speakers use least. It is correct but a little flat - fine for a stranger, oddly formal for someone you see daily. What people actually say is a greeting shaped to the group: 大家好 to a room, 老师好 to a teacher, 您好 to anyone you want to show respect. Learn the shape rather than the single word and you will sound placed rather than rehearsed.