I think a good Tag Wiki should cover the following topics :
The technical definition and a basic overview.
Why was the technology/technique/product needed, who developed it, when was it created.
A detailed description covering the various facets of the technique/technology.
Applications / Application Areas
Domains where the technology is used.
List of all the related tags for further exploration.
Frequently Asked Questions
The most common questions asked within the tag.
List of Tools/Software
The tools and software that is used for the technology/technique.
List Of Books/References segregated by targeted skill level (Beginner, Intermediate)
A curated list of books (ebook, print, free, paid), online references and tutorials.
Links to all the sources referred for the various areas of this Tag Wiki.
While writing a Tag Wiki, certain points should be covered first and only then should you move to other topics.
In the first phase, the focus should be clearly define what the tag is for and what it should be used for. The parts of the Wiki that should be covered first are Definition, Related Tags, Frequently Asked Questions and External Links. For certain tags, this should be enough, as there might not be more subject matter to explore.
Once these have been covered, the next stage of the process should be to expand on the subject matter. The aim should be to write a detailed description of the tag in a way that the concept becomes clear to new users* who may read the tag wiki. The topics that should be covered in this phase should be Detailed Explanation and Applications. If possible a short Background should also be provided. However, Background is optional as it may not be possible to explore this area for every tag.
In the last phase, the writer should work with other users to develop a List of Tools that are used for that concept, and a List of Books/References for the different expertise levels of users. This should be done via a meta post and should be kept updated. This should not be done simply on the basis of personal experience.
Once all of this has been covered, share your work proudly for everyone to see!
*By new users, I mean beginners of the subject matter, not the site.