Dungeons & Dragons/Developing a Campaign World
Developing a Campaign World 
One of the most important duties of a DM is to create the world the adventures occur within. Many settings have been published, notably the Forgotten Realms and Eberron worlds. However, many DMs chose to create their own worlds, or at least create a unique setting within a larger, established world. This section deals with those world creating for a single campaign setting, through several examples.
There are two primary approaches to creating a world from scratch, each with its own advantages and disadvantages.
- Focused Creation
- Broad World View
Focused Creation 
This method starts with a single point, usually a village or even an inn, and expands outwards to the kingdom, world, and planes used in the campaign. The advantage of this sort of campaign is that the players become very involved from the beginning in their location. Also, DMs have the ability to expand the world to suit the needs of the players. In this example, a DM develops a tavern that the characters will meet in for the first adventure, and expands it outwards from there.
The Single Point 
There are several key details a DM must address in creating the single point.
- Objects of interest
- Relevant game details
- How it fits into the bigger picture
The first thing to be resolved is the location itself. Is this a grimy, wooden shack with a thatched roof, or a marble palace?
Then, decide the objects within the place. Are there tables? Chairs? Potted plants? A fountain?
Decide upon the relevant game details. This can be the most time consuming step, but will vastly enhance the feeling of the in-game actions. Does the blinding sunlight give a penalty on attack rolls? How much damage does a beer bottle deal in a bar fight?
The mood is the most difficult to decide upon. How is this going to entice the players? What plot hooks can be found within the location, to start them on their quests?
Giving the Heroes some interesting and memorable people and entities to interact with is very high on the priority list of any game world designer. Having a villlain, a recurring merchant or informant, giving the impression that others are inhabiting the imaginary world along with the Players' characters.
1. Decide how the PCs came to that location. Is there a famous bard passing through? Are they out for a night of drinking, and happen to go to the same inn?
2. Flesh out each of the NPCs with enough backstory to pass by in a conversation. What's the bartender's name? What kind of beer does he like? Who's that guard outside the city gate? What is his attack, his AC? If it helps you can find any magazine or other source of photos, copy an image and then mod it to suit your needs, this should help you think about that persons mood, appearance, motivations, intellect, history, wealth etc. A short summary of each important NPC plus a picture showing them and notes on important possesssions or their role in the scheme of things. There need to be allies, patrons, victims to be rescued, dak hearted villains, light hearted comic relief, merchans, other adventurers, hangers on etc. Their will be families in the world, homes, shops, people travelling the roads, ships, farms, workshops, libraries, temples and palaces, all occupied by people with their own drives and effect on the PCs.
The required level of detail will depend upon your style and also the playing style of the adventurers. Don't be scared to wing it, but make notes and try to rationalise what the snap decision has led to: if it proves too unacceptable it can be overcome by numerous means such as killing off an NPC, sending them off to visit an aunt, illness, old age, or pretending that the unacceptable NPC was only acting out and was actually a spy or trickster etc.etc.
The bigger picture 
This is the least important of these steps, but it can help in the long run. Is this tavern on a big cross-country road? Is this forest threatened by loggers? Plant these ideas now. You can always change them if the campaign turns a different way.
Building Out 
It's perfectly alright to begin a Focused Creation with an idea of the world you want. Focus in on the single point, and use that as a template for other locations. If you make a palace, decide where the guards live, and then where the food comes from. Then, decide how the palace in the neighboring kingdom is different. Is the city built around the palace, or is it at the very edge of the city?
Use the ideas planted while developing the single point, and insert as many or as few as feels necessary for the players to have a feeling of where they are, and what you want them to do. Keep careful notes of rumors you plant, stories an NPC tells. If you mention that trolls are becoming more common in the north, remember it. The players may or may not take that lead, but it never fails to be safe.
Out-of game details can be changed easily, as long is there a suitable excuse. Changing something the PCs know can damage the realism of the campaign world, and make it less interesting, unless there is a reason that can be built into the campaign without changing something else. If everyone in the village knows it's against the King's Law to wear jewels, then that should be the same in every village in that kingdom, unless there is a special circumstance. If a small town is trying to become independent, and that is a focus of the campaign, feel free to have those townspeople ignore the law.
Rules changes should not be changed without a very good reason. If you decided all trees in your starting forest have 1000 HP, that is true for all trees in the world, unless they have been subjected to some form of dark magic, or weakened by drought, or some such world-shaking event. Make sure to make these changes apparent to the players: don't just say there was a drought because you want trees to be weaker. Poor townsfolk would die of thirst, raids by desert creatures would become more commonplace, and clerics would hold public prayers for rain.
Recurring Themes 
These are a DM's best friend. Add details to NPCs, places, and facts the PCs already know. If they find out the blacksmith who supplies them with cheap weapons used to work for another nation's army, their opinion on him may change. On a simpler level, they may simply see him every night in the tavern, telling stories about his son's work as a thatcher.
Don't overdo this, however. If every NPC has a shadowy past, or every forest is infested by a dark shadow, the characters will begin to note every single detail, which can take away from the gameplay and slow it down dramatically.
Interesting Places 
Spend time on each new place. Because you control how fast the PCs can move through the world, you control how much work you need to do to develop every new place. Don't go overboard, and try to make every location as detailed and important as the first. Keep a dozen details you want for every new location, and alter them for each new place. If your first druid enclave has a leader, make sure the next has a leader, although of a different level, a different name, a different background, etc.
Example of Focused Creation: "The Three Ears Tavern and Outwards" 
The Three Ears Tavern is a reasonably large, well kept tavern, although the thatch has a few holes and the sign is missing a few letters. It lies on the main road between Zuffeldorf and the Capital.