This step-by-step uses Statcounter as provider, but this probably applies to other providers too.
Most of the providers will guide you through the initial setup and provide a wizard to generate the tracking code
Default, most providers will generate scripted code.
The Wiki engine strips script when publishing or saving your article, so keep it simple. Stick to HTML.
The provider likely will use a wizard to generate the HTM code for you.
Trim the code, remove unnecessary info.
In fact, just keep the reference to the image source locaton (<img src=> tag).
TIP: in your tracking tag, remove the active hyperlink in HTML as it will show up in your Wiki article with an hyperlink icon.
Copy the trimmed HTML tag (from <a to </a>).
In the left below corner, click the HTML button.
Move to the end of the article.
Save the article
Your tracking tag should be invisible.
Once the page is published, you can start collecting data.
Or: see yourself (this is the public part of the stats page of this Wiki article)
(*) But feel free to use scripts or visible counters on your own blog, your own webspace, ....
Wiki feature request
If you would like to make this page obsolete, by including the essential page and author metrics natively to the Wiki interface: let us know and join the discussion on the Wiki Technet Forum.
See the section below for the applicable threads (but there are more...).