As I brought up in the comments of this question, it would be great if it were possible to somehow have a specified tag always be listed first on a post, or if certain special tags (in RPG.SE's case, system tags) always appeared first when applied to any post.
As SevenSidedDie pointed out in a comment there, adding any tag to a post that's more popular than the system tag:
demotes the system from the first tag spot, thus removing it from the page title and some Google searches.
This is obviously not ideal, hence my suggestion.
Please add a checkbox to the Tag Info page for moderators to mark a tag as "special", so that it is always sorted to be first on a post. (I imagine such a feature would be useful network-wide, but especially on RPG.SE.)
This would work like the four special tags on meta: all special tags are sorted by popularity first, then all normal tags are sorted by popularity.