there're a few ways that I prefer:
- download popular / high rating, or featured maps on this site and take a walk around, pay attention to the layout and the details.
- search for map theme that you prefer (e.g. abandoned industrial complex, Santorini, ..) on pinterest or YT, take inspiration from rl.
- learn from other fps games for layout ideas like the Quake series or Halo, Apex legends has a lot of cool stuff too.