High season brings thousands of tourists to tiny San Pedro. Residents, especially the indigenous Atacameño peoples, are sensitive to the overwhelming presence of outsiders. Make a special effort to behave appropriately and blend in as best you can; avoid wearing highly revealing clothes in town (save those bikinis for the hot springs), remove hats while visiting churches and consider wearing long pants. And don't take photographs of the people without asking for their permission first.
Water is scarce (obviously), so refrain from long soaks in the shower.