One of the skills I'm trying to hone as I am developing my campaign world is editing it. Leaving out details while they may be cool, not necessary at this time. Keep it focused and develop the cool stuff in small quantities so the players are not overwhelmed with information.
When I write up information for my world it tend to come in three different levels.
First, is the the overall definition.
Gorsdale - A mining village in the heart of the Formas Hills. It is run and protected by the merchant lord Tyberius.
Formas Hills - These hills are rough and unforgiving. The deadly, silver serpents make their home here, but because the ground is rich with ore people risk it all to find riches.
Tyberius - A merchant lord, friend of the king on sits on the council of the merchant guild. He is responsible for most of the mines in the southeast region of the kingdom.
Second, I get a little more specific with the information. Someone who has had some dealings with the person place or thing would know.
Gorsdale - This mining village is populated with slaves. Tyberius has the gold mine surrounded with his hired army, fortifications have been erected to protect from attack. No one is permitted entry.
Formas Hills - Some of the smaller hills are hollow and that's where the silver serpents make their home. Their skins are highly valued at the market and their poison is highly valued on the black market.
Tyberius - The merchant lord has no scruples about keeping and increasing his wealth. He owns a small army that he uses to intimidate others to get what he wants. Those who oppose him disappear or become very agreeable.
And the final stage I write something is more intimate details. Only those who have been there or dealt with the person for an extended period of time.
Gorsdale - Just as many wagon loads of corpses come out of Gorsdale as gold. The bodies are dumped in a pit a few miles away. Some of the corpses are marked with red. The pickers go through the corpses to find the marked bodies. It's inside these bodies that Tyberius hides the gems. The pickers gather the gems and bring them into town.
Formas Hills - There is a shrine in one of the hollowed hills. Its an ancient shrine with cryptic writings, but should some take the time to study they will find they no longer need to fear the silver serpents.
Tyberius - The gems he is smuggling out from his mines are what allows him to pay for his army. He sells most of his gems to the sea kingdoms as to not bring any unwanted attention. With his increase of power he's gotten a little sloppy and isn't focusing on his businesses and instead trying to become friends with nobility.
Not the best examples, but I think they demonstrate the different levels of information in a campaign. Some people and locations may only have two levels. A farmer in a village may only have one level, My name is Hank. I'm a farmer. I work the fields. His next level may be he works the north fields on odd days and south fields on even days.
Writing information like this helps me keep the places and people mysterious and have some depth. Players can assume, but it won't be until they start investigating that they'll find the next level of knowledge. And if your a good GM, they may regret knowing it.