The most important thing I know about world-building is that you have to do it.
There's no skipping it, even if you're writing contemporary fiction, or heck, even if you're writing contemporary nonfiction.
I often see world-building treated like it's reserved for fantasy or science fiction, but whenever you write a novel, or a memoir, or whatever, you're inviting readers to enter the world you've created, which is definitely a different world from the one your reader lives in (unless your book is a memoir and they actually lived it with you). Even different high schools in the same town have different cultures.
But world-building isn't a chore. Done right, it can be really fun to design the details of your characters' lives and interesting to try out things that are part of their world.
What do your characters eat? Eat that.
What books have they read? Read them.
What games do they play? Play them.
What music do they listen to? Listen to it.
How do they get in touch with other people? Try that. (If you can. I'm sure George R.R. Martin doesn't send people ravens and J.K. Rowling doesn't send letters by owl.)
I appreciate good world-building so much, especially in these rough times, when sometimes I just want to step out of this world and into another one for a while. What a gift you're giving your reader—to take them out of their world and immerse them in the one you've created, for a little while.