Be warned, though, that Stars and Star Production are different things. Some actions, like Clearing Forest, Whaling or selecting the resources when upgrading a level 2 city to level 3 return plain stars, whereas others like building Customs Houses or selecting Workshop when upgrading a level 1 city to level 2 will increase overall star production per turn (SPT).
The number of stars each city produces can be found at the right of the city name bar, next to the star icon. The player's capital generates an additional star per turn, and AI players' capitals have different bonuses based on the difficulty level.
Increasing Production
There are several ways to increase your SPT. Having a strong income of stars every turn is the backbone of a good empire. These are:
Levelling up Cities. Every time you level up a city, your SPT increases by 1.
Choosing the Workshop when you upgrade a city from Level 1 to Level 2 grants an additional 1 SPT.
Capturing Villages. Each village captured gives 1 SPT, as they become Level 1 cities.
Capturing enemy Cities. Capturing cities gives you the SPT it produced for the enemy (1 SPT per the city's level, -1 for each Anti-Food (red population), + 1 if the captured city has a Workshop.
Building Customs Houses. Customs Houses produce 2 SPT per adjacent Port. However, you can only build a maximum of one Customs House in a city's territory.
If playing as ∑∫ỹriȱŋ, you may build the Sanctuary. This produces 1 SPT for every adjacent wild animal, and attracts new wild animals to adjacent empty forests every 3 turns, useful for consistent income growth. However, you can only build a maximum of one Sanctuary in a city's territory.
If playing as Polaris, you may build the Ice Bank instead of a Customs House, which produces 3 SPT for every 20 frozen tiles (up to a maximum of 30 SPT). However, you can only build one Ice Bank.
One-Time Methods
These methods give a one-time boost of stars to your total. Be warned, for these are non-renewable. These are:
Choosing the Resources upgrade when you level up a city from Level 2 to Level 3. This grants 5 Stars.
Hunting Whales. This provides 10 stars per whale. You must have Whaling researched to do that.
Clearing Forest. This provides 2 stars per forest cleared. You must have Forestry researched to do that.
DisbandingUnits. This provides stars equal to half the amount spent to create the unit rounded down (e.g. Disbanding Knights gives 4 stars, but Disbanding Riders — only 1). You must have Free Spirit researched to do that.
If playing the Perfection, Glory or Might modes, meeting another player gives 5 stars before turn 10 and 10 stars after it (inclusive) if this tribe has no tech you are able to research right now.
Trivia
A screenshot from 2016 showing how stars used to be called "resources"
Stars were formerly known as "resources," as can be seen in the gameplay screenshot from 2016 on the right.
