Efficiently manage your demesne by acquiring valuable counties and duchies. More holdings mean more income potential.
Prioritize upgrading your own holdings before vassal-owned ones, as they directly contribute to your treasury.

Invest in buildings and improvements that boost income. These include trade posts, markets, mines, and farms.
Focus on upgrading buildings that increase tax income and levy size.

Research Cultural Innovations that enhance economic aspects like taxation, economy, and stewardship.
Adopt Economic Lifestyle perks that boost tax, control, and development growth.

Maintain high control levels in your counties to maximize tax income and avoid peasant uprisings.
Assign capable and content vassals to stewardship positions. High stewardship improves county income and reduces corruption.

Build and upgrade trade posts along major trade routes to gain substantial income. Choose a trade route with minimal competition.
Forming alliances and fostering positive relationships with neighboring rulers can lead to trade bonuses and economic benefits.

Arrange marriages strategically to inherit valuable titles and territories. More land means more income.
Ensure your heir is set up for financial success by marrying into wealthy families or securing alliances with powerful realms.

Raid neighboring territories for gold and captives during wars. This can be especially lucrative if you target wealthy areas.
Be cautious not to overextend your military, as the costs of maintaining a large army can outweigh the benefits.

Embark on pilgrimages or embark on quests. These can lead to valuable rewards, including gold and artifacts.
Participate in events and decisions that offer economic opportunities, such as establishing trade routes.

Assign a skilled steward to collect taxes in your capital, which can lead to a significant increase in income.
Appoint a competent spymaster to discover economic opportunities and schemes within your realm.

Convert to a culture or religion that offers economic benefits, like reduced building costs or increased trade income.
Participate in religious activities that provide financial rewards, such as tithing or religious taxation.

Remember that building a strong economy takes time and careful planning. Balancing your ambitions with financial stability is key to long-term success in Crusader Kings III. Adapt your strategies based on your realm's unique circumstances, and you'll soon become a wealthy and influential ruler. Good luck!