To give a personal example, a friend of mine came up with the idée of an island split between two factions. From that alone these is now a world, with its technologies, languages, magic, etc.

To get things more interesting, I imagined an Empire from which comes a faction. The Empire needed some background, so I created two continents, nations…

But to do that well, we needed a whole world to support it. Based on Artifexian's work, there is now a world, with its size, revolution period, so a calendar, etc.

And I've got plenty of notes, holy cow ! So my biggest advice is to organize yourself. Even if I like it extremely realistic, worldbuilding is hard because it requires a lot of knowledge.

Most tasks are independent, but can be used for others (ie. magic just exists, it is only a small part of a nation's lore but it will influence it). Some tasks will need others, though (ie. a calendar need astronomic cycles which need a planet and a sun). You will find ideas pretty much everywhere, you may want to keep notes.