(Note: You should at least be an admin or mod to promote the wiki. If you're not one of those, you should get permission from an admin or mod on that wiki to post a promotion.)
To promote a wiki, the following needs to be in your post:
For the title, it should say something like “Wiki Promotion: Wiki name”. This will tell people what the post is about and will increase your chances of your post being viewed.
For the post category, it should be in the “Wiki Introductions & Wiki Accomplishments” category. This will make it so users who are looking for new wikis to join will be able to find your post with more ease.
For the content of the post, you should answer the questions below:
What is your wiki called?
What is it about?
Why are you making a wiki about this topic?
Why might people want to join your community?
What have you written so far?
What do you want to do with the wiki in the future?
How could others help out?"
Where is it? (give a link!)
The information above can be found on this blog.
Your post should be at least 150 words long so that it abides by Community Central discussion guidelines.
It is recommended by this support article that you have at least 50 pages on your wiki.
As per Community Central Discussion guidelines, posts that offer admin/mod rights are not allowed.