A wiki is a place where people gather to collaborate. Like a meeting room or a living room, it gets cluttered after a little while. Another common metaphor is a garden, which gets overgrown without regular tending.
Spending small amounts of time gardening on a regular basis helps to make your wiki easy to navigate and a pleasant place to work.
Here are some techniques to use when you have some spare quality time to spend with the wiki. Add yours!
Pick some pages and clean them up -- correct misspellings, collect and condense comments, regularize the way lists or comments are formatted.
When you are working on a topic, find the relevant pages and make an index of those pages. These finder's aids are a long tradition in archives management where you need to quickly get to a few relevant documents mixed in with a large quantity of routine correspondence.
Add links from the home page to often-used index pages
Condense discussion into a statement of the end result, and add a link to the original discussion. See gardening, which was merged into this page.
Break long pages into meaningful sub-pages. Add links to the sub-pages from a main page.
Add existing pages to appropriate categories.
If you have old pages that you are no longer finding useful, make a link near the top of them to new pages that have more relevant information on the subject.
Remove obsolete material. Create linked archive pages if the material is useful
Everyone on the team can participate in continuous improvement. Depending on the structure of your team, it may make sense for one person to have special responsibility for maintaining a set of pages. Or it may make sense to have a designated gardener.
Gardening is most effective when it's done a bit at a time. Team members can take responsibility for making something they are working on more useful for everyone.
What to do about this wiki?
It's full of sandbox and testpages
It's especially bad, if normal words are also associated with garbage
Spend a few minutes with the CrapCollectorScript, and the site will become cleaner!
On long term, running an isolated playground.flexwiki.com would be good
It's full of senseless rename redirects
Delete all useless redirect pages, and leave only one, with the good name and good content!
Usefull pages with garbage injected
Inexperienced users accidentally edited the page, inserted text/templates and saved.
Misleading Title: and Summary: properties
Clear these!
Outdated or divergent "discussion" topics
Tough question what to do with them. Simply delete?
A wiki is a place where people gather to collaborate. Like a meeting room or a living room, it gets cluttered after a little while. Another common metaphor is a garden, which gets overgrown without regular tending. 
