My previous post, which you can find here, focused on the political structure and recent history of your world--whether kings or nobles rule your land, and whether wars have happened in recent decades. After the first three steps, you should be well on your way to illustrating your world's geography and knowing something of your world's inhabitants and what their racial relations are like. Once you've grasped at least the beginnings of those steps, feel free to move onto the final step in this series:
Step Four: Culture
In this step, it's time to flesh out how the inhabitants of your world live and interact on a daily basis. Is there a common language in your land? Are religious beliefs far-spread, or different in every region? How does each race believe your world was created? Do the poorer people act the same as those who are wealthy?
You may also want to consider the types of clothing and residences that are common in each region. Do elves wear rich robes, or thin fabrics? Do dwarves live in manor houses, or in holes in the earth?
Also, touch on the topic of magic. Are there wizards and magicians in your world? Can anyone do magic, or is it something that must be learned? What are the dangers? If you use a magic system, make sure that it doesn't make everything easy, or the challenges your characters face will not feel like challenges.
Take time considering whether there are cultural festivals in your world, and what the months and days of each year are called. Grasping the culture and tradition of your world allows for a rich story setting when you sit down to write your fantasy masterpiece. Each of the steps I've gone over so far will continue to develop as you write your story, but it is helpful to have a strong foundation before you even begin. Fantasy worlds must be complex and realistic, so don't rush the process of creating one. Patience will do you well in the end.
Now it's your turn--have you made up any languages or magic systems for your novel? How did you go about creating them?