"Add useful information"
This should be the mantra of all writers and editors here. It is your main purpose and guideline for what kinds of articles and information belong in this wiki. Add useful information. Err on the side of too much. If you want to add it, it's probably useful. Seriously, go to town.
Useful to whom? Users of this Wiki!
That's intentionally broad. In general, the more users who would benefit from the information you're adding, the better. But that is only one guideline!
An article about one obscure aspect of Erfworld that only a few people would care about is also useful! Even a deep and lengthy article on a topic that only half a dozen fans would ever care about makes the wiki better and more useful by existing than if it were not there to read.
And even an article which only the person who added it would find value in could STILL be useful, if it's something like personal reference page that you use to store information and references for future articles. But if you are the only person you could imagine getting value out of it, then consider whether it would be better if you kept it as notes on your own hard drive.
Useful how? Understanding and enjoying Erfworld!
Articles that help establish a frame of reference for the story can also be useful.
Articles about meta-facts, such as the creators, the fans, events related to Erfworld, the history of the project, press that the project has received, etc. are also useful and should be added.
What information isn't useful?
Misleading information isn't useful. Speculation that looks like fact needs to be clarified. Facts should be sourced when possible, but do not fall into the trap of classifying whole sources as off limits. Use common sense and reason. Challenge and research anything stated as fact which causes you to doubt it.
Completely irrelevant information isn't useful. But there will be a lot less of this than you think! If it has even a tangential use to fans of Erfworld, leave it in! Deletionism is Naughtymancy.
Spam isn't useful. Kill it with fire.
What about style?
A consistent style is useful. But enforcing a consistent style to the detriment of the usefulness of the tool is what has killed most of Wikipedia's awesome potential. So if you want to contribute your time cleaning up articles and making them clearer and more consistent, that is great! Please do! Just remember always that style is trumped by substance, and never hurt an article's utility in the name of improving its look and feel.
Some things you can do improve an article:
Make it clearer to understand, because that's useful.
Improve its organization, because that's useful.
Clean out redundant information, because that's useful.
Track down sources of facts, especially facts you question. That's useful not for its own sake, but for the sake of having an article with true information in it! If the information you're looking at is unsourced, but you have no reason to doubt it, then don't worry about it. We do not need to see "There are five fingers on the human hand." That's not helping.
In short, editors here should not get hung up on points of style. Don't give the slightest consideration to the word "encyclopedic" or anything similar. This wiki is not meant to be pretty, academic, or encyclopedic. It's meant to be comprehensive, dynamic, constructive, and helpful. If we eventually do get bogged down by trivia, then organize the trivia. Do not delete it!