Well, for me, when world building, I have to figure out what will be most important to the story and start there. Like, if the main character will need to be travelling a lot, making up interesting scenery and actual things of note, along with how the road system works, or with flying as the main mode of transportation, deciding what the flight is and how it is handled(Like do they fly on their own, or on flying cats or hover cars) how far apart things are, and so on. Or for another example, if the main point is, say, the need to gather something together, like my dad's "Rod of 7 Parts" which is used to seal the door of hell forever, the main focus should be coming up with these special places for the special items to be held or stored, what worldly obstacles you can put in the way. If the focus is more on the people, say it's about a kingdom or planet recovering from some catastrophe, then the focus would be around the people, and the need to find ways for the event to have affected the world would be more important than, say, the specifics of a mountain range that may or may not ever be seen.

so, that is the core of my input. Finding the center of whatever the story is about from within, and from there grow the world around it. Like, with our RP. Between us, the actual point IS world building, so we started with simple characters, nothing much going on, but with the steady will towards change we are growing it as naturally as we can through our avatars, feeling each other's intentions out, and our characters are building, growing, and evolving. We began with the natural elements, as all worlds must, and from there we will move on to creating more of the flavor, with our core of needing to build already having given us a world in which that very goal is quite comfortable and workable.

So, that's me talking naturally. I am quite out f my mind, so forgive me if it makes no sense, but that's what came to my mind first :P Enjoy :P