I basically set up an Excel doc for every campaign with:
-1 tab for PKs & important informations regarding the characters
-1 tab for the estates, lands & revenues
-1 tab for NPCs & family, allowing me to sort by family, household, PK relationship (wife, enemy, liege lord, etc)
-1 tab for the roll of years, with general/important events and more personal events
I also keep a simple campaign diary with the main events for each year.
All this helps me avoid blanks when suddenly, Bob the Quickly Named Uncle has to pop up on the spot in the game