Look for things in the world that have changed recently that might have created a new opportunity. Great example of this is DoorDash, which was started by undergrads at Stanford. You can also look for companies that have been successful recently and look for new variants on them. Nuvo Cargo is a good example of explicitly sitting down to try to think about startup ideas and actually finding a good one.
YC's Jared Friedman shares a framework for how to get and evaluate startup ideas. He delves into examples of YC companies and the inside stories of how they came up with the ideas that turned into billion-dollar companies. Even if you have an existing idea, this talk helps founders confirm that their idea is good and/or provides a framework for a future pivot.
Apply to Y Combinator: https://yc.link/SUS-apply
Work at a Startup: https://yc.link/SUS-jobs