A Good Dungeon Master has to be a Writer.
We've already seen that in the post of the 2nd January.
Don't matter here the skills to create plots and to describe correctly a scene, since they are storyteller's abilities.
A good writer is the one who's skillful in creating good a believable subjects.
When you create either a new setting or a campaign or a single place for an adventure, you use the same mental processes of a writer.
Let's see how to do.
Create only what you really need.
Don't write pages and pages about the world, the area or the continent where your players will move.
You can't know how the campaign story will develop itself, so you have high chances to do a lot of useless works.
So focus on creating only the indispensable things and create all the rest by improvisation when need will arise.
What is it really indispensable?
They're only the basic concepts, those characteristics which make unique what you have created.
What are those basic concepts?
Culture. All D&D settings are based upon some culture of present or past human history.
Typically it's the feudal era of Middle Ages but you can change a lot according to your imagination.
For example I'm a player (Yes, all DMs should also play as players, we'll look at in a future post) in a campaign whose culture of the region is a barbaric semi-civilized one.
Environment. Where will your players mainly move? In mountains? Forests of very high trees?
The area of the campaign is cold lands, rugged and wild with many icy places.
Think also about some important characteristics of the environment; close your eyes and imagine to be a dweller of that world: what do you see? What do you hear? What do you feel by your other senses?
Christian, the campaign's DM, has created many moons, of various size and colours, whose cycles keep the pace of the barbarians' lives.
Races and Classes. Are all available? Has anyone rules different from those written in the canon manuals?
In Christian's barbarian campaign only humans exists and Magic (both Arcane and Divine) is regarded as evil necromancy and its users are at best viewed with suspicion.
He has created also a couple of group whose goal is to fight against anything that's magical.
Situation. It's the simplest.
What's happening in the campaign (or world, region,...)?
If you cannot answer to this question you cannot be a DM yet.
I'm sure you can answer to it when you create something.
For example, in the campaign I'm playing some groups of strangers are coming to the barbarian region in order to conquer it.
Then take some of this basic concepts and develop them.
But also remember this Rule of the Good DM:
Everytime you create anything important for your campaign, devise also a secret related to it.
In the campaign I'm playing we've just discovered that a magical shield, which has been a main feature of the last 5-6 sessions, (we found it, we guarded it, we fought for it, we lost it and now we must find it again) contains the spirit of an immortal being who's revered by many as a deity.
Discovering secrets is the essence of the D&D game since the time when it was only the explorations of the Greyhawk dungeons.
When your players will discover a secret they'll have fune and they will come to the table because they will want for more.
If you'll make it happens you'll be a Good DM "Writer", like Christian.
P.S.: the basic concepts of Christian's campaign which I've said about are only a few of the many he's created. I thank him for the ideas he gave me to write this post.