It'll also help convince you that this world could exist. You are the first believer in it after all. Having worked things out in advance as to how things can work will also help against the dreaded "slump in the middle". You will already know what you need to know about your created world. You can focus on the drama of your story with that knowledge behind you.
1. System of Government. Draw a flowchart as to who runs what, what their powers are and how these feed in to each other (local government for example is always answerable to national government at some level).
2. The Need to Survive. Write out ten things your "people" need so they can survive. Draw a spider diagram of how they can obtain these things.
3. Cultures. Is your world going to be a mono-culture? If not, what other cultures are there? Draft ideas as to what these could be, how the multi cultures interact with each other (if they do at all), and whether there is any sense of superiority (justified or not) by one or more of these. If it is a mono-culture, were they always that way or have they driven others out?
Hope you have fun with these. Be as detailed or as scanty with details as you wish but the idea is this will give you something to refer to as you write your tale.