First of all I want to thank TheHoarseWhisperer for this thread, and everyone here for the comments.

I have my own way of world building, especially when I am building a RPG world, and I use both the top-down and bottom-up methods, following these 7 steps:

1. Universe creation: I make a quick scratch of my universe lifetime, when it begun, and where is it now in time.
1.a. Conected universe: My universe is never alone. I always say that is some other parallel (or connected) universe, but not how many, or how can someone travel between them (I only make that when I need it).

2. Star system: I choose how many stars (or suns), planets, and moons for the main planets.

3. The main planet: it's size, length of day, length of the year, seasons, and so on.
3.a. Natural satellite (moon): How many moons, distance to the moon (or moons), size of the moon, the moon cicle. If there is more than one moon, how the moons interact?

4. Planet's surface: I choose the main places, like the biggest country (or continent, or the most important one) and it's surroundings; I do the same for other places, if there will be several important countries (or kingdoms, or anything like that).
4.a. Tectonic plates: I make the plates that are near the main places.
4.b. Geography and Geology: I make a scratch of the boundaries, the mountain ranges, the forests, rivers and lakes, the minerals, the hazards, the politics, economy, and the cultures of the main places.

5. BOTTOM-UP: Now I choose a place to begin my story (and/or map), and make the details, like the place's history, the cultures, the main towns and cities, the economy, important people, heroes, local folk tales, and so on, trying to make it concise and "realistic" (or plausible).
5.b. Neighbors: I don't make all of them, just make some details like alliances and politics of the neighbor lands.

6. The plot: I create a main plot, an epic one, like the resurrection of an old evil god.
6.a. Political plot: I try to make something like a big war, conquest, or something more "mundane". Epic, but not as epic as a resurrection of a god.
6.b. The initial plot: I make the beginning of my campaign, where the players (or the characters) will start, and things like that.
6.c. Local plots: I make some local plots, to make sure I have an "emergency" story (or campaign).

7. The maps: this step is spread along the other ones, as I do the maps along with each phase of my project, but sometimes I make the maps only when I'm finished building the world.

The first three steps I did only once. With a few exceptions, I don't build another universe, I just use the one I made a long time ago, but do I change it when I need, to make improvements and corrections.

And to my main RPG setting I still use the same world, creating new places for new adventures, and making a world full of stories and heroes (and maps).

I am a RPG Game Master for about 12 years now, and I still didn't finish my main world, but I love improving it. I still have the first character sheets we'd used, and that chars are the world's greatest heroes of the today.

Hope this can help someone.