“When you build your campaign you will tailor it to suit your personal tastes. In the heat of play it will slowly evolve into a compound of your personality and those of your better participants, a superior alloy.” – DMG 7

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Work in progress.

A core part of old-school D&D is the DIY spirit, and that includes developing your own milieu for your game over the course of a long period of time. D&D shines in the long-term, ongoing campaign, backed by a game system that supports such play (for instance, AD&D). By planting your milieu's seeds, you prepare the fields for the cities, mountains, armies, dungeons, and dragons that will appear there over the course of time. Your seeds need not be more than a single settlement, a single dungeon, and a pantheon of modest size. From there, if you do it right, you will find that the world writes itself.

Early on, you will need to be able to have information on:

1. Deities and religion. (We have a pantheon of 17 core deities, one for each of the planes.)
2. A calendar.
3. Which multiclass and dual-class combinations are legal. (We allow all combinations as long as two classes of the same base class aren't mixed.)
4. What alignment looks like, and what in-world effects it has.
5. Where silver and cold iron weapons can be obtained.

Later on, you will want to have information on:

1. The number and nature of the suns, moons, and and any other relevant planets.
2. The nature of magic. Especially how druidic, paladin, and ranger magic works in your milieu.
3. How magic item manufacture and recharging magic items will work.
4. How do class-related guilds and organizations work, such as the thieves guild, assassins guild, druidic circles, and paladin orders.