I too enjoy the Navajo and Hopi country. The local radio station broadcasts in the Navajo language, and many of the business and highway signs are in two or three languages.
x2 on taking ANYONE's photo without permission. I do not care how cute the little girl looks in native dress -- get permission! Many of the tribal members still follow the native beliefs and religion, and taking someone's photo is stealing their soul. Very bad. Also watch what logos or sayings are on the t-shirt or hat you are wearing. That stylized corporate logo may be embarassingly similar to a bad luck or evil icon in the native beliefs. Best to stick plain unmarked clothing.
When touring the ruins be very respectful. Their ancestor's spirits still live there. And the ceremonial kivas are very interesting, but they are places of worship and respect them as you expect visitors to your church to act.