We're in the phase of the site where almost everyone can create new tags. However, there's an important part of a tag that often gets missed out when they get created: the wiki.
I have a rule for myself. If I create a tag, I have to demonstrate that it has value to the site, by writing the tag wiki. I'd like to ask that we all try to do something similar.
Currently, our tags page is full of non-wiki'd tags. I'm going through and editing some of them, but I can't get to all of them by any means. If you can help, please do - writing a tag wiki isn't necessarily onerous. If you don't have much time, just write the excerpt.
The excerpt is especially important because it comes up in the tag's hovercard. It's what defines how the tag should be used - if this explanation isn't there, people may well start using existing tags in ways they weren't intended.
So - if you create a tag, consider writing its wiki or excerpt; and if you've got some spare time, there are a lot of wikiless tags here.
(Note: when writing tag excerpts, the textbox will give you more characters than can actually fit in the hovercard. About one and a bit lines of text will fit; anything more will overflow.)