The best way to have startup ideas is to just notice them organically. If you look at the YC-1200 companies, at least 70% of them had their startup ideas organically rather than by like sitting down and explicitly trying to think of a startup idea.
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