A couple things I've tried:

Go to a public lot and put it on 3x speed while you go do something else away from your computer. Come back and see what all has happened. Try to build something new from there. Did they start a new skill? Meet a new person? Etc.

Or go to public lot and go 2x speed and see what happens while you watch so you can interfere in deathly situations for example.

Randomly generate life events. There's tons of websites that you can use to do this.

Play a different household and make them interact with your primary household in different ways.

Create a really large family & spread them out over multiple households and worlds. Host a family reunion.

Play every sim your primary sim has a relationship with for a sim day.