Never trust Montezuma. He can be “pleased” as punch with you, then turn on a dime and go all Pearl Harbor on your ass.
Giving up trade relations or entering a war with someone because another civ “demands” it is never a good idea. They’ll become best buddies again while you’re left holding the bag.
Technological progress is nice, but is trumped by brute manufacturing strength.
When you want to take a city, bring twice as many troops as you think you’ll need.
Despite some civs saying they’re “friendly”–you have no friends.