People talk about waiting to bet on the major stock and commodity bubbles before they crash, or getting in on the ground floor of the European trade companies, but those won't be around for 100 years, and if you're ready to get in on the ground floor of companies built around war and colonial exploitation, you might as well go all the way.
Join up with the Spanish military, get into the company of Cortes, and ingratiate yourself with him and his men.
Follow Cortes onto the mainland when he goes AWOL with his company. Witness and take part in the alliance building of the Aztec vassals against the empire and the takeover country. Try and distinguish yourself in battle so as to build a reputation. You are immortal after all, what do you have to lose?
Once the empire is subdued and blood runs in the streets, kill and replace Cortes. This should be done quietly if you have enough respect to replace him easily upon death and publicly if not to instill fear in the other men.
Become one of history's greatest monsters. Promote slavery, kill men over gold, and develop a reputation for cruelty that will discourage attempts at revolt. Generally warlord it up.
Quietly transfer wealth acquired in Latin America back to Europe under a number of false names and secret bank accounts and stage your own death, traveling back to Europe to look for more opportunities for expansion.
Having done this, you can create a new identity and get in a position to have a leading role in the VOC or the British East India Company, and inflict similar cruelty on different people with a few more layers of separation between their suffering and my wealth. Continue in this pattern until it becomes unprofitable to leverage human suffering for personal gain.
Or live a quiet life for ~400 years and attempt to become Bill Gates. That could work too.