Most of the time the logical advice to give to a game master looking to do some world building is to start from the beginning. Lay out the cosmos and the gods and the existential conflict inherent n the universe. That way, with such a foundation, you can lay brick after brick of detail, but is this the best way to build a world? Well I think that depends on the kind of world you want to build and in fact your world should not begin with a thought but instead with a (series of) question. So below I am going to spell out your Day 1 for World Building by offering up the questions that you want to ask yourself.
1. What is my purpose or reason for running this game? What is the important "IT" for running the game?
Why are you running the game in the first place? I assume through choice or getting the shortest straw that you are consenting to being the game master and world builder. With this in mind, what is the point of running THIS game and what do you want to get out of it?
It might be easier to answer the question if we prioritize aspects of the game and world.
Genre - Fantasy, Science Fiction, Horror, Modern, a combination
System - Class n Level, Skill based, Diceless, Narrative, FATE, Savage Worlds, etc...
Style - Traditional, Story heavy, GM-less, Minimalist
Fun - We just wanna roll dice twice a month for 3-5 hours
Story - Light, Heavy, Somber, Cynical
Deciding on the kind of game you are running and prioritizing some of the above should allow you to answer the question above. There may be more choices to consider, depending on your ideas/
2. Given your purpose, how big does the world need to be?
This is what I like to call Moorcock vs. Tolkien (or Jordan or Martin or Banks). Moorcok really only build what he needs in the moment, where the other authors here created huge worlds for their characters to inhabit. That sense of scope will help you narrow down what needs to come first. In Octavia Butler's Dawn, the protagonist starts out in a room. Just a single room. Of course there is a wider world, but the beginning of the story keeps you cooped up with the protagonist and her captors. This kind of intimate design calls for answering basic questions, but not elaborate creation myths. A little context for you as the game master is all that you need.
3. Given the scope of your game, what should the first thing you read or say to the players be?
Typically when starting a new campaign or even a one shot, my first question is "Did you guys bring me some Mt. Dew?". After that of course, I want to set the scene for the session (and campaign) with that opening monologue. When you have scope and purpose in mind, doing so is easy. So even before creating a central conflict, I jot down notes about the opening scene.
So let's put this all together. I am going to design a world as we go.
My purpose (other than as an example) is Style; I want to run a game that mixes 13th Warrior with The Wild Bunch. Given that, I want to keep the world relatively intimate to begin with. Starting small means I can add details as needed instead of creating tons of detail that might never be used. Of course I will likely need to do a great deal of improv along the way, but that is okay. I just means making notes.
Okay so our unnamed world has a purpose (Style) and is going to be small at first, just a little kingdom on a dusty plain or hidden amid rocky hills in a land similar to Medieval Spain. With that in mind, let's have a little introduction.
"A bell rings in the valley, mournful sounds that warn you to stay away. All along the dusty road move farmers and merchants, pulling mules or oxen up and down narrow paths. No one greets your arrival in the village beneath the king's keep, itself a small stone and wood affair. Guards stand sweltering in the unforgiving sun, wary of an armed traveler. You can see the bell now and the small stone chapel of the Hill Gods where the bell resides. Out front a procession of mostly women brush the dusty road with lilac as a body covered in linen is rolled into the courtyard. A man in brown robes waits with a torch aside a pyre."
Stay tuned for Day 2.
