While visiting the region of Sapa you will take many photos. Something you should remember is that local people are not here to entertain you. They are real people living their daily lives. Ask always for permission when taking portraits.
Ethnic minority people are kind, and welcome foreign visitors, but may be offended if you take a picture without permission. How would you react if someone took a picture of you on a monday morning and disappeared without even saying hello?
A sincere smile, may be the beginning of a short friendship. Remember that locals speak good English. You can learn many things about their daily lives if you ask them.