I’d add.

Don’t be afraid to mix in a little bit of science.

If you decide your fantasy world has multiple moons, consider how that affects the tides. Westeros is in a binary system, hence the multiple seasonal cycles.

Think about how elves or dwarves or whatever fantasy race you invent work at the biological level. Do they reproduce like humans or not? What’s their diet and how does that affect their culture.

Read some archaeological papers, too, to help get a grasp on how technology impacts culture. Then extrapolate that to magic.

If you put a tiny bit of science in the underpinnings of your world, you can then layer on the magic and it will feel much more grounded and stable to your readers.