Strategically Manage Estate Privileges and Reforms

Step-by-Step

Open the Government tab and review your estates.
Revoke harmful privileges from commoners (e.g., peasant levy size -50%), even if it costs stability.
Give beneficial privileges to commoners ("Common militias," "Communal lands"), clergy ("Religious administration," "Religious diplomats"), and chieftains ("Share of the spoils").
Be careful with powerful estates, especially chieftains—privileges to strong estates cost much more stability.
Aim to pull chieftain power below 25% and shift values away from aristocracy toward plutocracy for higher tax efficiency and lower court costs.
Add reforms and privileges to yourself for temporary bonuses, and regularly check for new estate and reform options.

Estate privileges control tax rates, rebellion risk, army size, and the direction of your government values.
Good choices here make your country stronger, richer, and more stable.