A wiki helps readers see relationships between ideas: what belongs together, what follows from what, and where exceptions apply. Its structure expresses those relationships, so the principles below outrank any practice built on them; the editing process is how an edit keeps them.
Qualities
Compact
A wiki is compact. People read it many times, so every extra word costs time and hides patterns: a sentence that could go without changing the point is not there.
The arrangement is a claim
A node's parent says what it belongs to; its siblings say what it can be compared with. A misplaced node teaches the wrong relationship even when its body is accurate.
So every node sits under the subject where a reader would look for it, and every section is there because its hierarchy helps the reader, not to fill a pattern.
A wiki does not disagree with itself
Each fact is stated in one addressable place, and the rest of the wiki links to it. Two places that say the same thing drift apart once one is edited, and a reader acts on whichever they found first.
Upkeep
A wiki decays, and from three directions
A wiki becomes stale when facts change, new exceptions appear, or the understanding of how topics relate changes. A current wiki has the fact, its boundary or its structure brought up to date by the very edit that revealed the change.
A wiki is tested by reading it
Checks catch common problems, but they cannot show that a page makes sense to its reader. A page is finished when it reads well whole, as its reader would read it, and a second reader has reviewed it.