The Aztec military lacked many of the commodities that European ones had for centuries like pack animals and dedicated wagon trains. But thanks to Spartan-like discipline and focused ferocity, the Aztecs were able to effectively defend and expand their empire generation after generation for centuries. Here's how one climbed from porter, the starting rank, to senior-most warrior.
New soldiers in the Aztec ranks worked as porters, standing in for the pack animals common in Europe. While this may seem demeaning by today's standards, the tough terrain and vegetation of the jungle made it challenging—if not impossible—to move large amounts of men and supplies without strong backs.
And, after serving as a porter to a more senior soldier or on the supply lines, they would advance to the novice rank and began fighting in support roles or apprenticed on the battlefield to a mentor. It was during this time that they would learn some maneuvers and how to pursue a fleeing enemy.
To advance further, it was necessary to begin capturing enemy troops. Quality and quantity counted, with enemy nobles being most prized.
As the soldier captured more and more enemy troops, he would get improved uniforms and weapons, eventually becoming a "Teacher of Youths" and then a "Ruler of Youths." Yes, do well enough in the army, and you were allowed to become a teacher like Rico in Starship Troopers.
If the soldier took a very important prisoner from an enemy force, they could now advance to captain.
This was the highest a commoner could climb unless they were granted honorary nobility due to an accomplishment in battle. Nobles, including honorary nobles, could be inducted into the Eagle and Jaguar fraternities. These warriors had special privileges and fine weapons.
Continuing to succeed would allow the soldier to climb to the Otomi, skilled and elite troops who wore special banners to symbolize their heroism. The only promotion beyond this was to "shorn one," the Cuahchiqueh. By this point, they were excluded from teaching at schools because their skills on the battlefield were simply too valuable.
Above all of these warriors were the king and his war council. The Masters of the House of Darts and the House of Darkness and the Cutter of Men were typically members of the royal family.
So, if you have a time machine and want to become a senior member of the Aztec army, remember to get adopted by the king or bring good weapons back with you, because you'll need to kidnap a lot of prestigious enemies in order to climb the ranks.