Window to Chiang Mai Thailand
The best time to visit a village is during a festival, especially the tribal New Year festivals, when the women and men are dressed in their finest costumes. The Lahu, Lisu and Yao hold their New Year festivals around the time of the Chinese New Year, which falls on the new moon of the second lunar month. The Hmong and the Akha have festivals in late December.
Times for festivals may vary between villages and clans as well as tribes. The Akha, for example, have their famous "swing" ceremony (August- September) 108 days after a rice-planting festival. The latter takes place when the village elders feel the time is right (May - June).
If you don't have a guide, it is best to know something of the customs, beliefs, and taboos before entering a village and be careful about what you touch. Otherwise how you should behave is probably a matter of common courtesy. Avoid scant clothing and ask permission before taking photos. If you stay in the village you should offer payment for accommodation.
Several books that explain the customs of each tribe in detail are locally available.
A Trekker's Guide to: The Hilltribes of Northern Thailand (John R. Davies, Footloose Books, UK. 1992) and Chiang Mai & The Hilltribes (Goldrich, Richard. Sangdad Publications, 1992) are both small enough to be taken on a trek. For in depth research, visit the library at the Tribal Research Institute at Chiang Mai University.