What are the best practices for creating a big world?

To clarify, I’m not building a fully functional game at the moment. I’m practicing with world creation. I’ve already taken a few courses on doing this stuff, just trying to get in some much needed practice. Hopefully in one year I’ll be a billionaire with the world’s most popular game lol (dreams). I have a lot of programming experience (in something different than C++ and Blueprints) and hoping that my programming aptitude will help when I need to use it in UE4.