Excellence in ADVICE
Just thought I should point some things out:
When building a world, it's impportant to remember that everything is based on everything else. That is an absolute law!
Let's start on the top and work down. And the top is *drum roll* GODS.
So, first thing to answer, does your world have god(s)?
Possible alteratives here are:
Yes, and people believe in it/them.
Yes, but people don't believe in it/them.
No, but people believe they do.
No, and no one thinks so, either.
Gods are important, because they dictate how your world probably was created. If you have gods, it's very probable that they created the world, and thus, you need to establish just why they did it, and you should establish the origin and purpose of the gods as well. It's not strictly necessary, but is a great help, especially later, when you create cultures. Peoples view on how their world was created is quite significant.
A simple example. The gods are an mysterious group of beings, devoted to create the perfect world.
The two alternatives for world creation are:
Scientific: Big bang, many years, lots of chaos, and so on. Mostly in worlds without gods.
Divine: Some gods decide that: Hey, let's go make a world. That sounds fun. Those gods have got to be drunk.
To continue the above example: Our example world was created by gods, as stated, because they want to create a perfect world. Logically, as these gods are not omni-anything, they work by trial and error.
So, the gods have created a world. And now, the REALLY important thing comes.
How does your world look? Enviroment is a major factor in how things develop, both biologically, and culturally. This applies even if all races are created by the gods. Those not suited WILL vanish. It's sensible to create life that actually is capable of survival. (of course, unsensible gods exist).
The example continious: The gods create a world with a single continent, dominated by forest. (I'm using a simple, one aspect eviroment for ease. You should do it much more complex. You hear me! *pointy finger*)
You probably want some sentient, even intelligent species in your world. Now is the time. They will of course be suited for their forest home. Which means that they probably won't be purely human. Face it, once we might have been kings of the trees, but now? It's a good laugh.
If you plan on using humans, remember that we actually are best suited for plains/ hills. Mountains is a no-go. Single individuals, yes. Whole human race, no.
Example (still the same): A sentient race is created for the forest. Based on previous experience, the gods make a race resembling a cross between cats and humanoids. They are agile enough, and have the natural equipment, for rapidly moving about in the forest.
At the same time as the sentiant race is created, the gods create several other types of non-sentient beings, to carry out natural functions, as outlined as necessary by earlier experiments. These are also all adapted to their forest home, which means they are all creatures capable of easily navigate the forest. So no elephants. I know there exist forest elephants, but they probably didn't start there. (I'm fully aware of the development of elephants, I'm refering to the size part of it.)
So, now we have a pantheon of gods, a functional world, plants and animals to keep it going, and a sentient specie to toy around with.
Society, culture and so on comes next week. That's my favourite part.
This is just a bit longer than I planned ^^'
And if someone thinks this fits better somewhere else, feel free to move it.