This is going to be attempt at a series of posts on world creation. Yes it has been done before, in painful excruciating detail elsewhere. Yes I am probably not the most eloquent writer to be making an attempt at it. Oh well, this is where I hang my thoughts to be read and hopefully critiqued.
So world creation. It is a daunting task, one that I have wholeheartedly embraced with my current campaign group, and one which I will continue to love for every campaign I run. The key part of this is to realize you need to only make one world (unless you do something to end said world, I would start over then). This is good, as making a fully fleshed out world is impossible. The world you create will never be as detailed as the one we live in, we simply can not invent thousands or millions of years of history, myths for hundred or thousands of cultures or any of the other details that make the world we live in so rich in detail. We may only scratch the surface and blow smoke, trusting in our audience to suspend their disbelief, ask only what they need to know to engage with the world to a reasonable degree and, forgive us for the holes and errors that come up during the course of the game.
So where to begin? How I started was to decide what type of games I would be playing in this world. I decided upon fantasy only. No steam punk, no westerns, no space, no sci-fi. This is necessary as the entire world must conform to a single genre, else there will be logic errors through out that will be hard to reconcile with the players. Now, many people my believe this restriction to be too limiting, but those people have limited imaginations, and don't realize that there are really only a limited number of plot lines any way [look here]. Also, think of all the mythology found in the Romans, Greeks, various oriental and middle eastern cultures, the cultures of the various native nations through out the world, the Vikings, and of the U.K alone, not to mention the rest of Europe. All of this is fantasy world material, and the variations of stories are endless.
So having picked a broad over arching "theme" for the world, I sat down and drew it out. Many people disagree with this being the next step I have found, but I thought it was helpful. Determine the general size of the world, [earth size?, bigger?, smaller?], determine what gimmick, if any, you wish to use in the world, I personally when with each pole being opposite not only magnetically but in light level, so one is always dark and one is always light.
Start by drawing the outline of the world, or if you are doing something like floating islands orbiting a point, the outline of the area the islands would be contained. Draw in control lines, such as the equator, the line above which the world is always dark, or below which it is always light, and any other control lines you think you would need. Follow this by drawing in the shapes of the largest terrestrial bodies that the world has, the continents basically. Make sure you make the shapes interesting, and fairly varied. I spent about 2 weeks deciding on the continental layout of my world before I was happy with the layout and variation between them all.
Next I will go through the process of how I filled out one continents general layout.