Below you’ll find a series of articles I wrote as a leadup to the release of book 1 of Obsidian and Blood, as very rough primers to the basic Aztec setting.

• Obsidian and Blood setting, 1: the Valley of Mexico
• Obsidian and Blood setting, 2: Tenochtitlan
• Obsidian and Blood setting, 3: The Sacred Precinct
• Obsidian and Blood setting, 4: Acatl and death in Mexica religion
• Maps

BTW, the usual disclaimer applies, and it applies even more here, because there are so few books written in Mesoamerica, and much as I love my novels, I don’t want them to be held out as some sort of historical reference. I’m quite happy seeing them as Mesoamerican fantasy, but…
See, I’m a writer–not a historian, not a researcher. I did my best with a mountain of sources, but I’m no expert and no Nahuatl, so it’s highly possible (and, indeed, highly probable) that the Obsidian and Blood books include some mistakes.
If you want references about Aztec life in the 1480s, can I suggest the work of people like Miguel Leon-Portilla or David Carrasco.
Or, to put it another way: my books are awesome, reasonably well-researched fantasy, but very bad primary sources.

A few online sources on the Nahuatl people:

• Museo Nacional de Antropologia (webpage in Spanish)
• The Nahua Newsletter
• The International Indian Treaty Council
• American Indian Movement
• Survival International
• University of Texas at Austin
• University of Oklahoma